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| |
| <section id="dataframes"> |
| <h1>DataFrames<a class="headerlink" href="#dataframes" title="Link to this heading">¶</a></h1> |
| <section id="overview"> |
| <h2>Overview<a class="headerlink" href="#overview" title="Link to this heading">¶</a></h2> |
| <p>DataFusion’s DataFrame API provides a powerful interface for building and executing queries against data sources. |
| It offers a familiar API similar to pandas and other DataFrame libraries, but with the performance benefits of Rust |
| and Arrow.</p> |
| <p>A DataFrame represents a logical plan that can be composed through operations like filtering, projection, and aggregation. |
| The actual execution happens when terminal operations like <code class="docutils literal notranslate"><span class="pre">collect()</span></code> or <code class="docutils literal notranslate"><span class="pre">show()</span></code> are called.</p> |
| </section> |
| <section id="basic-usage"> |
| <h2>Basic Usage<a class="headerlink" href="#basic-usage" title="Link to this heading">¶</a></h2> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">datafusion</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">col</span><span class="p">,</span> <span class="n">lit</span> |
| |
| <span class="c1"># Create a context and register a data source</span> |
| <span class="n">ctx</span> <span class="o">=</span> <span class="n">datafusion</span><span class="o">.</span><span class="n">SessionContext</span><span class="p">()</span> |
| <span class="n">ctx</span><span class="o">.</span><span class="n">register_csv</span><span class="p">(</span><span class="s2">"my_table"</span><span class="p">,</span> <span class="s2">"path/to/data.csv"</span><span class="p">)</span> |
| |
| <span class="c1"># Create and manipulate a DataFrame</span> |
| <span class="n">df</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">sql</span><span class="p">(</span><span class="s2">"SELECT * FROM my_table"</span><span class="p">)</span> |
| |
| <span class="c1"># Or use the DataFrame API directly</span> |
| <span class="n">df</span> <span class="o">=</span> <span class="p">(</span><span class="n">ctx</span><span class="o">.</span><span class="n">table</span><span class="p">(</span><span class="s2">"my_table"</span><span class="p">)</span> |
| <span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">col</span><span class="p">(</span><span class="s2">"age"</span><span class="p">)</span> <span class="o">></span> <span class="n">lit</span><span class="p">(</span><span class="mi">25</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">"name"</span><span class="p">),</span> <span class="n">col</span><span class="p">(</span><span class="s2">"age"</span><span class="p">)]))</span> |
| |
| <span class="c1"># Execute and collect results</span> |
| <span class="n">result</span> <span class="o">=</span> <span class="n">df</span><span class="o">.</span><span class="n">collect</span><span class="p">()</span> |
| |
| <span class="c1"># Display the first few rows</span> |
| <span class="n">df</span><span class="o">.</span><span class="n">show</span><span class="p">()</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="html-rendering"> |
| <h2>HTML Rendering<a class="headerlink" href="#html-rendering" title="Link to this heading">¶</a></h2> |
| <p>When working in Jupyter notebooks or other environments that support HTML rendering, DataFrames will |
| automatically display as formatted HTML tables, making it easier to visualize your data.</p> |
| <p>The <code class="docutils literal notranslate"><span class="pre">_repr_html_</span></code> method is called automatically by Jupyter to render a DataFrame. This method |
| controls how DataFrames appear in notebook environments, providing a richer visualization than |
| plain text output.</p> |
| </section> |
| <section id="customizing-html-rendering"> |
| <h2>Customizing HTML Rendering<a class="headerlink" href="#customizing-html-rendering" title="Link to this heading">¶</a></h2> |
| <p>You can customize how DataFrames are rendered in HTML by configuring the formatter:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.html_formatter</span><span class="w"> </span><span class="kn">import</span> <span class="n">configure_formatter</span> |
| |
| <span class="c1"># Change the default styling</span> |
| <span class="n">configure_formatter</span><span class="p">(</span> |
| <span class="n">max_cell_length</span><span class="o">=</span><span class="mi">25</span><span class="p">,</span> <span class="c1"># Maximum characters in a cell before truncation</span> |
| <span class="n">max_width</span><span class="o">=</span><span class="mi">1000</span><span class="p">,</span> <span class="c1"># Maximum width in pixels</span> |
| <span class="n">max_height</span><span class="o">=</span><span class="mi">300</span><span class="p">,</span> <span class="c1"># Maximum height in pixels</span> |
| <span class="n">max_memory_bytes</span><span class="o">=</span><span class="mi">2097152</span><span class="p">,</span> <span class="c1"># Maximum memory for rendering (2MB)</span> |
| <span class="n">min_rows_display</span><span class="o">=</span><span class="mi">20</span><span class="p">,</span> <span class="c1"># Minimum number of rows to display</span> |
| <span class="n">repr_rows</span><span class="o">=</span><span class="mi">10</span><span class="p">,</span> <span class="c1"># Number of rows to display in __repr__</span> |
| <span class="n">enable_cell_expansion</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span><span class="c1"># Allow expanding truncated cells</span> |
| <span class="n">custom_css</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="c1"># Additional custom CSS</span> |
| <span class="n">show_truncation_message</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="c1"># Show message when data is truncated</span> |
| <span class="n">style_provider</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="c1"># Custom styling provider</span> |
| <span class="n">use_shared_styles</span><span class="o">=</span><span class="kc">True</span> <span class="c1"># Share styles across tables</span> |
| <span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>The formatter settings affect all DataFrames displayed after configuration.</p> |
| </section> |
| <section id="custom-style-providers"> |
| <h2>Custom Style Providers<a class="headerlink" href="#custom-style-providers" title="Link to this heading">¶</a></h2> |
| <p>For advanced styling needs, you can create a custom style provider:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.html_formatter</span><span class="w"> </span><span class="kn">import</span> <span class="n">StyleProvider</span><span class="p">,</span> <span class="n">configure_formatter</span> |
| |
| <span class="k">class</span><span class="w"> </span><span class="nc">MyStyleProvider</span><span class="p">(</span><span class="n">StyleProvider</span><span class="p">):</span> |
| <span class="k">def</span><span class="w"> </span><span class="nf">get_table_styles</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> |
| <span class="k">return</span> <span class="p">{</span> |
| <span class="s2">"table"</span><span class="p">:</span> <span class="s2">"border-collapse: collapse; width: 100%;"</span><span class="p">,</span> |
| <span class="s2">"th"</span><span class="p">:</span> <span class="s2">"background-color: #007bff; color: white; padding: 8px; text-align: left;"</span><span class="p">,</span> |
| <span class="s2">"td"</span><span class="p">:</span> <span class="s2">"border: 1px solid #ddd; padding: 8px;"</span><span class="p">,</span> |
| <span class="s2">"tr:nth-child(even)"</span><span class="p">:</span> <span class="s2">"background-color: #f2f2f2;"</span><span class="p">,</span> |
| <span class="p">}</span> |
| |
| <span class="k">def</span><span class="w"> </span><span class="nf">get_value_styles</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dtype</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span> |
| <span class="w"> </span><span class="sd">"""Return custom styles for specific values"""</span> |
| <span class="k">if</span> <span class="n">dtype</span> <span class="o">==</span> <span class="s2">"float"</span> <span class="ow">and</span> <span class="n">value</span> <span class="o"><</span> <span class="mi">0</span><span class="p">:</span> |
| <span class="k">return</span> <span class="s2">"color: red;"</span> |
| <span class="k">return</span> <span class="kc">None</span> |
| |
| <span class="c1"># Apply the custom style provider</span> |
| <span class="n">configure_formatter</span><span class="p">(</span><span class="n">style_provider</span><span class="o">=</span><span class="n">MyStyleProvider</span><span class="p">())</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="performance-optimization-with-shared-styles"> |
| <h2>Performance Optimization with Shared Styles<a class="headerlink" href="#performance-optimization-with-shared-styles" title="Link to this heading">¶</a></h2> |
| <p>The <code class="docutils literal notranslate"><span class="pre">use_shared_styles</span></code> parameter (enabled by default) optimizes performance when displaying |
| multiple DataFrames in notebook environments:</p> |
| <blockquote> |
| <div></div></blockquote> |
| <p>When <code class="docutils literal notranslate"><span class="pre">use_shared_styles=True</span></code>: |
| - CSS styles and JavaScript are included only once per notebook session |
| - This reduces HTML output size and prevents style duplication |
| - Improves rendering performance with many DataFrames |
| - Applies consistent styling across all DataFrames</p> |
| </section> |
| <section id="creating-a-custom-formatter"> |
| <h2>Creating a Custom Formatter<a class="headerlink" href="#creating-a-custom-formatter" title="Link to this heading">¶</a></h2> |
| <p>For complete control over rendering, you can implement a custom formatter:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.html_formatter</span><span class="w"> </span><span class="kn">import</span> <span class="n">Formatter</span><span class="p">,</span> <span class="n">get_formatter</span> |
| |
| <span class="k">class</span><span class="w"> </span><span class="nc">MyFormatter</span><span class="p">(</span><span class="n">Formatter</span><span class="p">):</span> |
| <span class="k">def</span><span class="w"> </span><span class="nf">format_html</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">batches</span><span class="p">,</span> <span class="n">schema</span><span class="p">,</span> <span class="n">has_more</span><span class="o">=</span><span class="kc">False</span><span class="p">,</span> <span class="n">table_uuid</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span> |
| <span class="c1"># Create your custom HTML here</span> |
| <span class="n">html</span> <span class="o">=</span> <span class="s2">"<div class='my-custom-table'>"</span> |
| <span class="c1"># ... formatting logic ...</span> |
| <span class="n">html</span> <span class="o">+=</span> <span class="s2">"</div>"</span> |
| <span class="k">return</span> <span class="n">html</span> |
| |
| <span class="c1"># Set as the global formatter</span> |
| <span class="n">configure_formatter</span><span class="p">(</span><span class="n">formatter_class</span><span class="o">=</span><span class="n">MyFormatter</span><span class="p">)</span> |
| |
| <span class="c1"># Or use the formatter just for specific operations</span> |
| <span class="n">formatter</span> <span class="o">=</span> <span class="n">get_formatter</span><span class="p">()</span> |
| <span class="n">custom_html</span> <span class="o">=</span> <span class="n">formatter</span><span class="o">.</span><span class="n">format_html</span><span class="p">(</span><span class="n">batches</span><span class="p">,</span> <span class="n">schema</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="managing-formatters"> |
| <h2>Managing Formatters<a class="headerlink" href="#managing-formatters" title="Link to this heading">¶</a></h2> |
| <p>Reset to default formatting:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.html_formatter</span><span class="w"> </span><span class="kn">import</span> <span class="n">reset_formatter</span> |
| |
| <span class="c1"># Reset to default settings</span> |
| <span class="n">reset_formatter</span><span class="p">()</span> |
| </pre></div> |
| </div> |
| <p>Get the current formatter settings:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.html_formatter</span><span class="w"> </span><span class="kn">import</span> <span class="n">get_formatter</span> |
| |
| <span class="n">formatter</span> <span class="o">=</span> <span class="n">get_formatter</span><span class="p">()</span> |
| <span class="nb">print</span><span class="p">(</span><span class="n">formatter</span><span class="o">.</span><span class="n">max_rows</span><span class="p">)</span> |
| <span class="nb">print</span><span class="p">(</span><span class="n">formatter</span><span class="o">.</span><span class="n">theme</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="contextual-formatting"> |
| <h2>Contextual Formatting<a class="headerlink" href="#contextual-formatting" title="Link to this heading">¶</a></h2> |
| <p>You can also use a context manager to temporarily change formatting settings:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">datafusion.html_formatter</span><span class="w"> </span><span class="kn">import</span> <span class="n">formatting_context</span> |
| |
| <span class="c1"># Default formatting</span> |
| <span class="n">df</span><span class="o">.</span><span class="n">show</span><span class="p">()</span> |
| |
| <span class="c1"># Temporarily use different formatting</span> |
| <span class="k">with</span> <span class="n">formatting_context</span><span class="p">(</span><span class="n">max_rows</span><span class="o">=</span><span class="mi">100</span><span class="p">,</span> <span class="n">theme</span><span class="o">=</span><span class="s2">"dark"</span><span class="p">):</span> |
| <span class="n">df</span><span class="o">.</span><span class="n">show</span><span class="p">()</span> <span class="c1"># Will use the temporary settings</span> |
| |
| <span class="c1"># Back to default formatting</span> |
| <span class="n">df</span><span class="o">.</span><span class="n">show</span><span class="p">()</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="memory-and-display-controls"> |
| <h2>Memory and Display Controls<a class="headerlink" href="#memory-and-display-controls" title="Link to this heading">¶</a></h2> |
| <p>You can control how much data is displayed and how much memory is used for rendering:</p> |
| <blockquote> |
| <div><div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">configure_formatter</span><span class="p">(</span> |
| <span class="n">max_memory_bytes</span><span class="o">=</span><span class="mi">4</span> <span class="o">*</span> <span class="mi">1024</span> <span class="o">*</span> <span class="mi">1024</span><span class="p">,</span> <span class="c1"># 4MB maximum memory for display</span> |
| <span class="n">min_rows_display</span><span class="o">=</span><span class="mi">50</span><span class="p">,</span> <span class="c1"># Always show at least 50 rows</span> |
| <span class="n">repr_rows</span><span class="o">=</span><span class="mi">20</span> <span class="c1"># Show 20 rows in __repr__ output</span> |
| <span class="p">)</span> |
| </pre></div> |
| </div> |
| </div></blockquote> |
| <p>These parameters help balance comprehensive data display against performance considerations.</p> |
| </section> |
| </section> |
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