blob: f2358ca39ce7f07f63db62ac21d561b55bbaaeb6 [file] [log] [blame]
<!DOCTYPE html>
<html lang="en" data-content_root="../../">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
<title>Expressions &#8212; Apache Arrow DataFusion documentation</title>
<link href="../../_static/styles/theme.css?digest=1999514e3f237ded88cf" rel="stylesheet">
<link href="../../_static/styles/pydata-sphinx-theme.css?digest=1999514e3f237ded88cf" rel="stylesheet">
<link rel="stylesheet"
href="../../_static/vendor/fontawesome/5.13.0/css/all.min.css">
<link rel="preload" as="font" type="font/woff2" crossorigin
href="../../_static/vendor/fontawesome/5.13.0/webfonts/fa-solid-900.woff2">
<link rel="preload" as="font" type="font/woff2" crossorigin
href="../../_static/vendor/fontawesome/5.13.0/webfonts/fa-brands-400.woff2">
<link rel="stylesheet" type="text/css" href="../../_static/pygments.css?v=8f2a1f02" />
<link rel="stylesheet" type="text/css" href="../../_static/styles/pydata-sphinx-theme.css?v=1140d252" />
<link rel="stylesheet" type="text/css" href="../../_static/graphviz.css?v=4ae1632d" />
<link rel="stylesheet" type="text/css" href="../../_static/theme_overrides.css?v=dca7052a" />
<link rel="preload" as="script" href="../../_static/scripts/pydata-sphinx-theme.js?digest=1999514e3f237ded88cf">
<script src="../../_static/documentation_options.js?v=8a448e45"></script>
<script src="../../_static/doctools.js?v=9bcbadda"></script>
<script src="../../_static/sphinx_highlight.js?v=dc90522c"></script>
<link rel="index" title="Index" href="../../genindex.html" />
<link rel="search" title="Search" href="../../search.html" />
<link rel="next" title="Joins" href="joins.html" />
<link rel="prev" title="Column Selections" href="select-and-filter.html" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<meta name="docsearch:language" content="en">
<!-- Google Analytics -->
</head>
<body data-spy="scroll" data-target="#bd-toc-nav" data-offset="80">
<div class="container-fluid" id="banner"></div>
<div class="container-xl">
<div class="row">
<!-- Only show if we have sidebars configured, else just a small margin -->
<div class="col-12 col-md-3 bd-sidebar">
<div class="sidebar-start-items">
<a class="navbar-brand" href="../../index.html">
<img src="../../_static/images/2x_bgwhite_original.png" class="logo" alt="logo">
</a>
<form class="bd-search d-flex align-items-center" action="../../search.html" method="get">
<i class="icon fas fa-search"></i>
<input type="search" class="form-control" name="q" id="search-input" placeholder="Search the docs ..." aria-label="Search the docs ..." autocomplete="off" >
</form>
<nav class="bd-links" id="bd-docs-nav" aria-label="Main navigation">
<div class="bd-toc-item active">
<p aria-level="2" class="caption" role="heading">
<span class="caption-text">
LINKS
</span>
</p>
<ul class="nav bd-sidenav">
<li class="toctree-l1">
<a class="reference external" href="https://github.com/apache/datafusion-python">
Github and Issue Tracker
</a>
</li>
<li class="toctree-l1">
<a class="reference external" href="https://docs.rs/datafusion/latest/datafusion/">
Rust's API Docs
</a>
</li>
<li class="toctree-l1">
<a class="reference external" href="https://github.com/apache/datafusion/blob/main/CODE_OF_CONDUCT.md">
Code of conduct
</a>
</li>
<li class="toctree-l1">
<a class="reference external" href="https://github.com/apache/datafusion-python/tree/main/examples">
Examples
</a>
</li>
</ul>
<p aria-level="2" class="caption" role="heading">
<span class="caption-text">
USER GUIDE
</span>
</p>
<ul class="current nav bd-sidenav">
<li class="toctree-l1">
<a class="reference internal" href="../introduction.html">
Introduction
</a>
</li>
<li class="toctree-l1">
<a class="reference internal" href="../basics.html">
Concepts
</a>
</li>
<li class="toctree-l1">
<a class="reference internal" href="../data-sources.html">
Data Sources
</a>
</li>
<li class="toctree-l1 has-children">
<a class="reference internal" href="../dataframe/index.html">
DataFrames
</a>
<input class="toctree-checkbox" id="toctree-checkbox-1" name="toctree-checkbox-1" type="checkbox"/>
<label for="toctree-checkbox-1">
<i class="fas fa-chevron-down">
</i>
</label>
<ul>
<li class="toctree-l2">
<a class="reference internal" href="../dataframe/rendering.html">
HTML Rendering in Jupyter
</a>
</li>
</ul>
</li>
<li class="toctree-l1 current active has-children">
<a class="reference internal" href="index.html">
Common Operations
</a>
<input checked="" class="toctree-checkbox" id="toctree-checkbox-2" name="toctree-checkbox-2" type="checkbox"/>
<label for="toctree-checkbox-2">
<i class="fas fa-chevron-down">
</i>
</label>
<ul class="current">
<li class="toctree-l2">
<a class="reference internal" href="views.html">
Registering Views
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="basic-info.html">
Basic Operations
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="select-and-filter.html">
Column Selections
</a>
</li>
<li class="toctree-l2 current active">
<a class="current reference internal" href="#">
Expressions
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="joins.html">
Joins
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="functions.html">
Functions
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="aggregations.html">
Aggregation
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="windows.html">
Window Functions
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="udf-and-udfa.html">
User-Defined Functions
</a>
</li>
</ul>
</li>
<li class="toctree-l1 has-children">
<a class="reference internal" href="../io/index.html">
IO
</a>
<input class="toctree-checkbox" id="toctree-checkbox-3" name="toctree-checkbox-3" type="checkbox"/>
<label for="toctree-checkbox-3">
<i class="fas fa-chevron-down">
</i>
</label>
<ul>
<li class="toctree-l2">
<a class="reference internal" href="../io/arrow.html">
Arrow
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="../io/avro.html">
Avro
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="../io/csv.html">
CSV
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="../io/json.html">
JSON
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="../io/parquet.html">
Parquet
</a>
</li>
<li class="toctree-l2">
<a class="reference internal" href="../io/table_provider.html">
Custom Table Provider
</a>
</li>
</ul>
</li>
<li class="toctree-l1">
<a class="reference internal" href="../configuration.html">
Configuration
</a>
</li>
<li class="toctree-l1">
<a class="reference internal" href="../sql.html">
SQL
</a>
</li>
</ul>
<p aria-level="2" class="caption" role="heading">
<span class="caption-text">
CONTRIBUTOR GUIDE
</span>
</p>
<ul class="nav bd-sidenav">
<li class="toctree-l1">
<a class="reference internal" href="../../contributor-guide/introduction.html">
Introduction
</a>
</li>
<li class="toctree-l1">
<a class="reference internal" href="../../contributor-guide/ffi.html">
Python Extensions
</a>
</li>
</ul>
<p aria-level="2" class="caption" role="heading">
<span class="caption-text">
API
</span>
</p>
<ul class="nav bd-sidenav">
<li class="toctree-l1 has-children">
<a class="reference internal" href="../../autoapi/index.html">
API Reference
</a>
<input class="toctree-checkbox" id="toctree-checkbox-4" name="toctree-checkbox-4" type="checkbox"/>
<label for="toctree-checkbox-4">
<i class="fas fa-chevron-down">
</i>
</label>
<ul>
<li class="toctree-l2 has-children">
<a class="reference internal" href="../../autoapi/datafusion/index.html">
datafusion
</a>
<input class="toctree-checkbox" id="toctree-checkbox-5" name="toctree-checkbox-5" type="checkbox"/>
<label for="toctree-checkbox-5">
<i class="fas fa-chevron-down">
</i>
</label>
<ul>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/catalog/index.html">
datafusion.catalog
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/context/index.html">
datafusion.context
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/dataframe/index.html">
datafusion.dataframe
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/dataframe_formatter/index.html">
datafusion.dataframe_formatter
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/expr/index.html">
datafusion.expr
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/functions/index.html">
datafusion.functions
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/html_formatter/index.html">
datafusion.html_formatter
</a>
</li>
<li class="toctree-l3 has-children">
<a class="reference internal" href="../../autoapi/datafusion/input/index.html">
datafusion.input
</a>
<input class="toctree-checkbox" id="toctree-checkbox-6" name="toctree-checkbox-6" type="checkbox"/>
<label for="toctree-checkbox-6">
<i class="fas fa-chevron-down">
</i>
</label>
<ul>
<li class="toctree-l4">
<a class="reference internal" href="../../autoapi/datafusion/input/base/index.html">
datafusion.input.base
</a>
</li>
<li class="toctree-l4">
<a class="reference internal" href="../../autoapi/datafusion/input/location/index.html">
datafusion.input.location
</a>
</li>
</ul>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/io/index.html">
datafusion.io
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/object_store/index.html">
datafusion.object_store
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/plan/index.html">
datafusion.plan
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/record_batch/index.html">
datafusion.record_batch
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/substrait/index.html">
datafusion.substrait
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/unparser/index.html">
datafusion.unparser
</a>
</li>
<li class="toctree-l3">
<a class="reference internal" href="../../autoapi/datafusion/user_defined/index.html">
datafusion.user_defined
</a>
</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</nav>
</div>
<div class="sidebar-end-items">
</div>
</div>
<div class="d-none d-xl-block col-xl-2 bd-toc">
<div class="toc-item">
<div class="tocsection onthispage pt-5 pb-3">
<i class="fas fa-list"></i> On this page
</div>
<nav id="bd-toc-nav">
<ul class="visible nav section-nav flex-column">
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#column">
Column
</a>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#literal">
Literal
</a>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#boolean">
Boolean
</a>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#arrays">
Arrays
</a>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#structs">
Structs
</a>
</li>
<li class="toc-h2 nav-item toc-entry">
<a class="reference internal nav-link" href="#functions">
Functions
</a>
</li>
</ul>
</nav>
</div>
<div class="toc-item">
</div>
</div>
<main class="col-12 col-md-9 col-xl-7 py-md-5 pl-md-5 pr-md-4 bd-content" role="main">
<div>
<section id="expressions">
<span id="id1"></span><h1>Expressions<a class="headerlink" href="#expressions" title="Link to this heading">¶</a></h1>
<p>In DataFusion an expression is an abstraction that represents a computation.
Expressions are used as the primary inputs and outputs for most functions within
DataFusion. As such, expressions can be combined to create expression trees, a
concept shared across most compilers and databases.</p>
<section id="column">
<h2>Column<a class="headerlink" href="#column" title="Link to this heading">¶</a></h2>
<p>The first expression most new users will interact with is the Column, which is created by calling <a class="reference internal" href="../../autoapi/datafusion/index.html#datafusion.col" title="datafusion.col"><code class="xref py py-func docutils literal notranslate"><span class="pre">col()</span></code></a>.
This expression represents a column within a DataFrame. The function <a class="reference internal" href="../../autoapi/datafusion/index.html#datafusion.col" title="datafusion.col"><code class="xref py py-func docutils literal notranslate"><span class="pre">col()</span></code></a> takes as in input a string
and returns an expression as it’s output.</p>
</section>
<section id="literal">
<h2>Literal<a class="headerlink" href="#literal" title="Link to this heading">¶</a></h2>
<p>Literal expressions represent a single value. These are helpful in a wide range of operations where
a specific, known value is of interest. You can create a literal expression using the function <a class="reference internal" href="../../autoapi/datafusion/index.html#datafusion.lit" title="datafusion.lit"><code class="xref py py-func docutils literal notranslate"><span class="pre">lit()</span></code></a>.
The type of the object passed to the <a class="reference internal" href="../../autoapi/datafusion/index.html#datafusion.lit" title="datafusion.lit"><code class="xref py py-func docutils literal notranslate"><span class="pre">lit()</span></code></a> function will be used to convert it to a known data type.</p>
<p>In the following example we create expressions for the column named <cite>color</cite> and the literal scalar string <cite>red</cite>.
The resultant variable <cite>red_units</cite> is itself also an expression.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">1</span><span class="p">]:</span> <span class="n">red_units</span> <span class="o">=</span> <span class="n">col</span><span class="p">(</span><span class="s2">&quot;color&quot;</span><span class="p">)</span> <span class="o">==</span> <span class="n">lit</span><span class="p">(</span><span class="s2">&quot;red&quot;</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="boolean">
<h2>Boolean<a class="headerlink" href="#boolean" title="Link to this heading">¶</a></h2>
<p>When combining expressions that evaluate to a boolean value, you can combine these expressions using boolean operators.
It is important to note that in order to combine these expressions, you <em>must</em> use bitwise operators. See the following
examples for the and, or, and not operations.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">2</span><span class="p">]:</span> <span class="n">red_or_green_units</span> <span class="o">=</span> <span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;color&quot;</span><span class="p">)</span> <span class="o">==</span> <span class="n">lit</span><span class="p">(</span><span class="s2">&quot;red&quot;</span><span class="p">))</span> <span class="o">|</span> <span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;color&quot;</span><span class="p">)</span> <span class="o">==</span> <span class="n">lit</span><span class="p">(</span><span class="s2">&quot;green&quot;</span><span class="p">))</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">3</span><span class="p">]:</span> <span class="n">heavy_red_units</span> <span class="o">=</span> <span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;color&quot;</span><span class="p">)</span> <span class="o">==</span> <span class="n">lit</span><span class="p">(</span><span class="s2">&quot;red&quot;</span><span class="p">))</span> <span class="o">&amp;</span> <span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;weight&quot;</span><span class="p">)</span> <span class="o">&gt;</span> <span class="n">lit</span><span class="p">(</span><span class="mi">42</span><span class="p">))</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">4</span><span class="p">]:</span> <span class="n">not_red_units</span> <span class="o">=</span> <span class="o">~</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;color&quot;</span><span class="p">)</span> <span class="o">==</span> <span class="n">lit</span><span class="p">(</span><span class="s2">&quot;red&quot;</span><span class="p">))</span>
</pre></div>
</div>
</section>
<section id="arrays">
<h2>Arrays<a class="headerlink" href="#arrays" title="Link to this heading">¶</a></h2>
<p>For columns that contain arrays of values, you can access individual elements of the array by index
using bracket indexing. This is similar to calling the function
<a class="reference internal" href="../../autoapi/datafusion/functions/index.html#datafusion.functions.array_element" title="datafusion.functions.array_element"><code class="xref py py-func docutils literal notranslate"><span class="pre">datafusion.functions.array_element()</span></code></a>, except that array indexing using brackets is 0 based,
similar to Python arrays and <code class="docutils literal notranslate"><span class="pre">array_element</span></code> is 1 based indexing to be compatible with other SQL
approaches.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">5</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">SessionContext</span><span class="p">,</span> <span class="n">col</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">6</span><span class="p">]:</span> <span class="n">ctx</span> <span class="o">=</span> <span class="n">SessionContext</span><span class="p">()</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">7</span><span class="p">]:</span> <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">from_pydict</span><span class="p">({</span><span class="s2">&quot;a&quot;</span><span class="p">:</span> <span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">]]})</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">8</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;a&quot;</span><span class="p">)[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;a0&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">8</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+----+</span>
<span class="o">|</span> <span class="n">a0</span> <span class="o">|</span>
<span class="o">+----+</span>
<span class="o">|</span> <span class="mi">1</span> <span class="o">|</span>
<span class="o">|</span> <span class="mi">4</span> <span class="o">|</span>
<span class="o">+----+</span>
</pre></div>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Indexing an element of an array via <code class="docutils literal notranslate"><span class="pre">[]</span></code> starts at index 0 whereas
<a class="reference internal" href="../../autoapi/datafusion/functions/index.html#datafusion.functions.array_element" title="datafusion.functions.array_element"><code class="xref py py-func docutils literal notranslate"><span class="pre">array_element()</span></code></a> starts at index 1.</p>
</div>
<p>Starting in DataFusion 49.0.0 you can also create slices of array elements using
slice syntax from Python.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">9</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;a&quot;</span><span class="p">)[</span><span class="mi">1</span><span class="p">:</span><span class="mi">3</span><span class="p">]</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;second_two_elements&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">9</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+---------------------+</span>
<span class="o">|</span> <span class="n">second_two_elements</span> <span class="o">|</span>
<span class="o">+---------------------+</span>
<span class="o">|</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span> <span class="o">|</span>
<span class="o">|</span> <span class="p">[</span><span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">]</span> <span class="o">|</span>
<span class="o">+---------------------+</span>
</pre></div>
</div>
<p>To check if an array is empty, you can use the function <a class="reference internal" href="../../autoapi/datafusion/functions/index.html#datafusion.functions.array_empty" title="datafusion.functions.array_empty"><code class="xref py py-func docutils literal notranslate"><span class="pre">datafusion.functions.array_empty()</span></code></a> or <cite>datafusion.functions.empty</cite>.
This function returns a boolean indicating whether the array is empty.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">SessionContext</span><span class="p">,</span> <span class="n">col</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.functions</span><span class="w"> </span><span class="kn">import</span> <span class="n">array_empty</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">12</span><span class="p">]:</span> <span class="n">ctx</span> <span class="o">=</span> <span class="n">SessionContext</span><span class="p">()</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">13</span><span class="p">]:</span> <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">from_pydict</span><span class="p">({</span><span class="s2">&quot;a&quot;</span><span class="p">:</span> <span class="p">[[],</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]]})</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">14</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">array_empty</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;a&quot;</span><span class="p">))</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;is_empty&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">14</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+----------+</span>
<span class="o">|</span> <span class="n">is_empty</span> <span class="o">|</span>
<span class="o">+----------+</span>
<span class="o">|</span> <span class="n">true</span> <span class="o">|</span>
<span class="o">|</span> <span class="n">false</span> <span class="o">|</span>
<span class="o">+----------+</span>
</pre></div>
</div>
<p>In this example, the <cite>is_empty</cite> column will contain <cite>True</cite> for the first row and <cite>False</cite> for the second row.</p>
<p>To get the total number of elements in an array, you can use the function <a class="reference internal" href="../../autoapi/datafusion/functions/index.html#datafusion.functions.cardinality" title="datafusion.functions.cardinality"><code class="xref py py-func docutils literal notranslate"><span class="pre">datafusion.functions.cardinality()</span></code></a>.
This function returns an integer indicating the total number of elements in the array.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">15</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">SessionContext</span><span class="p">,</span> <span class="n">col</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">16</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.functions</span><span class="w"> </span><span class="kn">import</span> <span class="n">cardinality</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">17</span><span class="p">]:</span> <span class="n">ctx</span> <span class="o">=</span> <span class="n">SessionContext</span><span class="p">()</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">18</span><span class="p">]:</span> <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">from_pydict</span><span class="p">({</span><span class="s2">&quot;a&quot;</span><span class="p">:</span> <span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">]]})</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">19</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">cardinality</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;a&quot;</span><span class="p">))</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;num_elements&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">19</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+--------------+</span>
<span class="o">|</span> <span class="n">num_elements</span> <span class="o">|</span>
<span class="o">+--------------+</span>
<span class="o">|</span> <span class="mi">3</span> <span class="o">|</span>
<span class="o">|</span> <span class="mi">3</span> <span class="o">|</span>
<span class="o">+--------------+</span>
</pre></div>
</div>
<p>In this example, the <cite>num_elements</cite> column will contain <cite>3</cite> for both rows.</p>
<p>To concatenate two arrays, you can use the function <a class="reference internal" href="../../autoapi/datafusion/functions/index.html#datafusion.functions.array_cat" title="datafusion.functions.array_cat"><code class="xref py py-func docutils literal notranslate"><span class="pre">datafusion.functions.array_cat()</span></code></a> or <a class="reference internal" href="../../autoapi/datafusion/functions/index.html#datafusion.functions.array_concat" title="datafusion.functions.array_concat"><code class="xref py py-func docutils literal notranslate"><span class="pre">datafusion.functions.array_concat()</span></code></a>.
These functions return a new array that is the concatenation of the input arrays.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">20</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">SessionContext</span><span class="p">,</span> <span class="n">col</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">21</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.functions</span><span class="w"> </span><span class="kn">import</span> <span class="n">array_cat</span><span class="p">,</span> <span class="n">array_concat</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">22</span><span class="p">]:</span> <span class="n">ctx</span> <span class="o">=</span> <span class="n">SessionContext</span><span class="p">()</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">23</span><span class="p">]:</span> <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">from_pydict</span><span class="p">({</span><span class="s2">&quot;a&quot;</span><span class="p">:</span> <span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]],</span> <span class="s2">&quot;b&quot;</span><span class="p">:</span> <span class="p">[[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">]]})</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">24</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">array_cat</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;a&quot;</span><span class="p">),</span> <span class="n">col</span><span class="p">(</span><span class="s2">&quot;b&quot;</span><span class="p">))</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;concatenated_array&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">24</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+--------------------+</span>
<span class="o">|</span> <span class="n">concatenated_array</span> <span class="o">|</span>
<span class="o">+--------------------+</span>
<span class="o">|</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">]</span> <span class="o">|</span>
<span class="o">+--------------------+</span>
</pre></div>
</div>
<p>In this example, the <cite>concatenated_array</cite> column will contain <cite>[1, 2, 3, 4, 5, 6]</cite>.</p>
<p>To repeat the elements of an array a specified number of times, you can use the function <a class="reference internal" href="../../autoapi/datafusion/functions/index.html#datafusion.functions.array_repeat" title="datafusion.functions.array_repeat"><code class="xref py py-func docutils literal notranslate"><span class="pre">datafusion.functions.array_repeat()</span></code></a>.
This function returns a new array with the elements repeated.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">25</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">SessionContext</span><span class="p">,</span> <span class="n">col</span><span class="p">,</span> <span class="n">literal</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">26</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.functions</span><span class="w"> </span><span class="kn">import</span> <span class="n">array_repeat</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">27</span><span class="p">]:</span> <span class="n">ctx</span> <span class="o">=</span> <span class="n">SessionContext</span><span class="p">()</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">28</span><span class="p">]:</span> <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">from_pydict</span><span class="p">({</span><span class="s2">&quot;a&quot;</span><span class="p">:</span> <span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]]})</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">29</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">array_repeat</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;a&quot;</span><span class="p">),</span> <span class="n">literal</span><span class="p">(</span><span class="mi">2</span><span class="p">))</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;repeated_array&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">29</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+------------------------+</span>
<span class="o">|</span> <span class="n">repeated_array</span> <span class="o">|</span>
<span class="o">+------------------------+</span>
<span class="o">|</span> <span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]]</span> <span class="o">|</span>
<span class="o">+------------------------+</span>
</pre></div>
</div>
<p>In this example, the <cite>repeated_array</cite> column will contain <cite>[[1, 2, 3], [1, 2, 3]]</cite>.</p>
</section>
<section id="structs">
<h2>Structs<a class="headerlink" href="#structs" title="Link to this heading">¶</a></h2>
<p>Columns that contain struct elements can be accessed using the bracket notation as if they were
Python dictionary style objects. This expects a string key as the parameter passed.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">30</span><span class="p">]:</span> <span class="n">ctx</span> <span class="o">=</span> <span class="n">SessionContext</span><span class="p">()</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">31</span><span class="p">]:</span> <span class="n">data</span> <span class="o">=</span> <span class="p">{</span><span class="s2">&quot;a&quot;</span><span class="p">:</span> <span class="p">[{</span><span class="s2">&quot;size&quot;</span><span class="p">:</span> <span class="mi">15</span><span class="p">,</span> <span class="s2">&quot;color&quot;</span><span class="p">:</span> <span class="s2">&quot;green&quot;</span><span class="p">},</span> <span class="p">{</span><span class="s2">&quot;size&quot;</span><span class="p">:</span> <span class="mi">10</span><span class="p">,</span> <span class="s2">&quot;color&quot;</span><span class="p">:</span> <span class="s2">&quot;blue&quot;</span><span class="p">}]}</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">32</span><span class="p">]:</span> <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">from_pydict</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">33</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;a&quot;</span><span class="p">)[</span><span class="s2">&quot;size&quot;</span><span class="p">]</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;a_size&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">33</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+--------+</span>
<span class="o">|</span> <span class="n">a_size</span> <span class="o">|</span>
<span class="o">+--------+</span>
<span class="o">|</span> <span class="mi">15</span> <span class="o">|</span>
<span class="o">|</span> <span class="mi">10</span> <span class="o">|</span>
<span class="o">+--------+</span>
</pre></div>
</div>
</section>
<section id="functions">
<h2>Functions<a class="headerlink" href="#functions" title="Link to this heading">¶</a></h2>
<p>As mentioned before, most functions in DataFusion return an expression at their output. This allows us to create
a wide variety of expressions built up from other expressions. For example, <a class="reference internal" href="../../autoapi/datafusion/expr/index.html#datafusion.expr.Expr.alias" title="datafusion.expr.Expr.alias"><code class="xref py py-func docutils literal notranslate"><span class="pre">alias()</span></code></a> is a function that takes
as it input a single expression and returns an expression in which the name of the expression has changed.</p>
<p>The following example shows a series of expressions that are built up from functions operating on expressions.</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">34</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">SessionContext</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">35</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">column</span><span class="p">,</span> <span class="n">lit</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">36</span><span class="p">]:</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datafusion</span><span class="w"> </span><span class="kn">import</span> <span class="n">functions</span> <span class="k">as</span> <span class="n">f</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">37</span><span class="p">]:</span> <span class="kn">import</span><span class="w"> </span><span class="nn">random</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">38</span><span class="p">]:</span> <span class="n">ctx</span> <span class="o">=</span> <span class="n">SessionContext</span><span class="p">()</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">39</span><span class="p">]:</span> <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">from_pydict</span><span class="p">(</span>
<span class="o">....</span><span class="p">:</span> <span class="p">{</span>
<span class="o">....</span><span class="p">:</span> <span class="s2">&quot;name&quot;</span><span class="p">:</span> <span class="p">[</span><span class="s2">&quot;Albert&quot;</span><span class="p">,</span> <span class="s2">&quot;Becca&quot;</span><span class="p">,</span> <span class="s2">&quot;Carlos&quot;</span><span class="p">,</span> <span class="s2">&quot;Dante&quot;</span><span class="p">],</span>
<span class="o">....</span><span class="p">:</span> <span class="s2">&quot;age&quot;</span><span class="p">:</span> <span class="p">[</span><span class="mi">42</span><span class="p">,</span> <span class="mi">67</span><span class="p">,</span> <span class="mi">27</span><span class="p">,</span> <span class="mi">71</span><span class="p">],</span>
<span class="o">....</span><span class="p">:</span> <span class="s2">&quot;years_in_position&quot;</span><span class="p">:</span> <span class="p">[</span><span class="mi">13</span><span class="p">,</span> <span class="mi">21</span><span class="p">,</span> <span class="mi">10</span><span class="p">,</span> <span class="mi">54</span><span class="p">],</span>
<span class="o">....</span><span class="p">:</span> <span class="p">},</span>
<span class="o">....</span><span class="p">:</span> <span class="n">name</span><span class="o">=</span><span class="s2">&quot;employees&quot;</span>
<span class="o">....</span><span class="p">:</span> <span class="p">)</span>
<span class="o">....</span><span class="p">:</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">40</span><span class="p">]:</span> <span class="n">age_col</span> <span class="o">=</span> <span class="n">col</span><span class="p">(</span><span class="s2">&quot;age&quot;</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">41</span><span class="p">]:</span> <span class="n">renamed_age</span> <span class="o">=</span> <span class="n">age_col</span><span class="o">.</span><span class="n">alias</span><span class="p">(</span><span class="s2">&quot;age_in_years&quot;</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">42</span><span class="p">]:</span> <span class="n">start_age</span> <span class="o">=</span> <span class="n">age_col</span> <span class="o">-</span> <span class="n">col</span><span class="p">(</span><span class="s2">&quot;years_in_position&quot;</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">43</span><span class="p">]:</span> <span class="n">started_young</span> <span class="o">=</span> <span class="n">start_age</span> <span class="o">&lt;</span> <span class="n">lit</span><span class="p">(</span><span class="mi">18</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">44</span><span class="p">]:</span> <span class="n">can_retire</span> <span class="o">=</span> <span class="n">age_col</span> <span class="o">&gt;</span> <span class="n">lit</span><span class="p">(</span><span class="mi">65</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">45</span><span class="p">]:</span> <span class="n">long_timer</span> <span class="o">=</span> <span class="n">started_young</span> <span class="o">&amp;</span> <span class="n">can_retire</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">46</span><span class="p">]:</span> <span class="n">df</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">long_timer</span><span class="p">)</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">&quot;name&quot;</span><span class="p">),</span> <span class="n">renamed_age</span><span class="p">,</span> <span class="n">col</span><span class="p">(</span><span class="s2">&quot;years_in_position&quot;</span><span class="p">))</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">46</span><span class="p">]:</span>
<span class="n">DataFrame</span><span class="p">()</span>
<span class="o">+-------+--------------+-------------------+</span>
<span class="o">|</span> <span class="n">name</span> <span class="o">|</span> <span class="n">age_in_years</span> <span class="o">|</span> <span class="n">years_in_position</span> <span class="o">|</span>
<span class="o">+-------+--------------+-------------------+</span>
<span class="o">|</span> <span class="n">Dante</span> <span class="o">|</span> <span class="mi">71</span> <span class="o">|</span> <span class="mi">54</span> <span class="o">|</span>
<span class="o">+-------+--------------+-------------------+</span>
</pre></div>
</div>
</section>
</section>
</div>
<!-- Previous / next buttons -->
<div class='prev-next-area'>
<a class='left-prev' id="prev-link" href="select-and-filter.html" title="previous page">
<i class="fas fa-angle-left"></i>
<div class="prev-next-info">
<p class="prev-next-subtitle">previous</p>
<p class="prev-next-title">Column Selections</p>
</div>
</a>
<a class='right-next' id="next-link" href="joins.html" title="next page">
<div class="prev-next-info">
<p class="prev-next-subtitle">next</p>
<p class="prev-next-title">Joins</p>
</div>
<i class="fas fa-angle-right"></i>
</a>
</div>
</main>
</div>
</div>
<script src="../../_static/scripts/pydata-sphinx-theme.js?digest=1999514e3f237ded88cf"></script>
<!-- Based on pydata_sphinx_theme/footer.html -->
<footer class="footer mt-5 mt-md-0">
<div class="container">
<div class="footer-item">
<p class="copyright">
&copy; Copyright 2019-2024, Apache Software Foundation.<br>
</p>
</div>
<div class="footer-item">
<p class="sphinx-version">
Created using <a href="http://sphinx-doc.org/">Sphinx</a> 8.1.3.<br>
</p>
</div>
<div class="footer-item">
<p>Apache Arrow DataFusion, Arrow DataFusion, Apache, the Apache feather logo, and the Apache Arrow DataFusion project logo</p>
<p>are either registered trademarks or trademarks of The Apache Software Foundation in the United States and other countries.</p>
</div>
</div>
</footer>
</body>
</html>