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 <meta property="og:title" content="Open a multi-file dataset — open_dataset" />
 <meta property="og:description" content="Arrow Datasets allow you to query against data that has been split across
 multiple files. This sharding of data may indicate partitioning, which
 can accelerate queries that only touch some partitions (files). Call
 open_dataset() to point to a directory of data files and return a
 Dataset, then use dplyr methods to query it." />


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 <div class="row">
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     <div class="page-header">
     <h1>Open a multi-file dataset</h1>
     <small class="dont-index">Source: <a href='https://github.com/apache/arrow/blob/master/r/R/dataset.R'><code>R/dataset.R</code></a></small>
     <div class="hidden name"><code>open_dataset.Rd</code></div>
     </div>

     <div class="ref-description">
     <p>Arrow Datasets allow you to query against data that has been split across
 multiple files. This sharding of data may indicate partitioning, which
 can accelerate queries that only touch some partitions (files). Call
 <code>open_dataset()</code> to point to a directory of data files and return a
 <code>Dataset</code>, then use <code>dplyr</code> methods to query it.</p>
     </div>

     <pre class="usage"><span class='fu'>open_dataset</span><span class='op'>(</span>
   <span class='va'>sources</span>,
   schema <span class='op'>=</span> <span class='cn'>NULL</span>,
   partitioning <span class='op'>=</span> <span class='fu'><a href='hive_partition.html'>hive_partition</a></span><span class='op'>(</span><span class='op'>)</span>,
   unify_schemas <span class='op'>=</span> <span class='cn'>NULL</span>,
   <span class='va'>...</span>
 <span class='op'>)</span></pre>

     <h2 class="hasAnchor" id="arguments"><a class="anchor" href="#arguments"></a>Arguments</h2>
     <table class="ref-arguments">
     <colgroup><col class="name" /><col class="desc" /></colgroup>
     <tr>
       <th>sources</th>
       <td><p>One of:</p><ul>
 <li><p>a string path or URI to a directory containing data files</p></li>
 <li><p>a string path or URI to a single file</p></li>
 <li><p>a character vector of paths or URIs to individual data files</p></li>
 <li><p>a list of <code>Dataset</code> objects as created by this function</p></li>
 <li><p>a list of <code>DatasetFactory</code> objects as created by <code><a href='dataset_factory.html'>dataset_factory()</a></code>.</p></li>
 </ul>

 <p>When <code>sources</code> is a vector of file URIs, they must all use the same protocol
 and point to files located in the same file system and having the same
 format.</p></td>
     </tr>
     <tr>
       <th>schema</th>
       <td><p><a href='Schema.html'>Schema</a> for the <code>Dataset</code>. If <code>NULL</code> (the default), the schema
 will be inferred from the data sources.</p></td>
     </tr>
     <tr>
       <th>partitioning</th>
       <td><p>When <code>sources</code> is a directory path/URI, one of:</p><ul>
 <li><p>a <code>Schema</code>, in which case the file paths relative to <code>sources</code> will be
 parsed, and path segments will be matched with the schema fields. For
 example, <code><a href='Schema.html'>schema(year = int16(), month = int8())</a></code> would create partitions
 for file paths like <code>"2019/01/file.parquet"</code>, <code>"2019/02/file.parquet"</code>,
 etc.</p></li>
 <li><p>a character vector that defines the field names corresponding to those
 path segments (that is, you're providing the names that would correspond
 to a <code>Schema</code> but the types will be autodetected)</p></li>
 <li><p>a <code>HivePartitioning</code> or <code>HivePartitioningFactory</code>, as returned
 by <code><a href='hive_partition.html'>hive_partition()</a></code> which parses explicit or autodetected fields from
 Hive-style path segments</p></li>
 <li><p><code>NULL</code> for no partitioning</p></li>
 </ul>

 <p>The default is to autodetect Hive-style partitions. When <code>sources</code> is not a
 directory path/URI, <code>partitioning</code> is ignored.</p></td>
     </tr>
     <tr>
       <th>unify_schemas</th>
       <td><p>logical: should all data fragments (files, <code>Dataset</code>s)
 be scanned in order to create a unified schema from them? If <code>FALSE</code>, only
 the first fragment will be inspected for its schema. Use this fast path
 when you know and trust that all fragments have an identical schema.
 The default is <code>FALSE</code> when creating a dataset from a directory path/URI or
 vector of file paths/URIs (because there may be many files and scanning may
 be slow) but <code>TRUE</code> when <code>sources</code> is a list of <code>Dataset</code>s (because there
 should be few <code>Dataset</code>s in the list and their <code>Schema</code>s are already in
 memory).</p></td>
     </tr>
     <tr>
       <th>...</th>
       <td><p>additional arguments passed to <code><a href='dataset_factory.html'>dataset_factory()</a></code> when <code>sources</code>
 is a directory path/URI or vector of file paths/URIs, otherwise ignored.
 These may include <code>format</code> to indicate the file format, or other
 format-specific options.</p></td>
     </tr>
     </table>

     <h2 class="hasAnchor" id="value"><a class="anchor" href="#value"></a>Value</h2>

     <p>A <a href='Dataset.html'>Dataset</a> R6 object. Use <code>dplyr</code> methods on it to query the data,
 or call <code><a href='Scanner.html'>$NewScan()</a></code> to construct a query directly.</p>
     <h2 class="hasAnchor" id="see-also"><a class="anchor" href="#see-also"></a>See also</h2>

     <div class='dont-index'><p><code><a href='../articles/dataset.html'>vignette("dataset", package = "arrow")</a></code></p></div>

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	<meta property="og:description" content="Arrow Datasets allow you to query against data that has been split across
	multiple files. This sharding of data may indicate partitioning, which
	can accelerate queries that only touch some partitions (files). Call
	open_dataset() to point to a directory of data files and return a
	Dataset, then use dplyr methods to query it." />




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	</header>

	<div class="row">
	<div class="col-md-9 contents">
	<div class="page-header">
	<h1>Open a multi-file dataset</h1>
	<small class="dont-index">Source: <a href='https://github.com/apache/arrow/blob/master/r/R/dataset.R'><code>R/dataset.R</code></a></small>
	<div class="hidden name"><code>open_dataset.Rd</code></div>
	</div>

	<div class="ref-description">
	<p>Arrow Datasets allow you to query against data that has been split across
	multiple files. This sharding of data may indicate partitioning, which
	can accelerate queries that only touch some partitions (files). Call
	<code>open_dataset()</code> to point to a directory of data files and return a
	<code>Dataset</code>, then use <code>dplyr</code> methods to query it.</p>
	</div>

	<pre class="usage"><span class='fu'>open_dataset</span><span class='op'>(</span>
	<span class='va'>sources</span>,
	schema <span class='op'>=</span> <span class='cn'>NULL</span>,
	partitioning <span class='op'>=</span> <span class='fu'><a href='hive_partition.html'>hive_partition</a></span><span class='op'>(</span><span class='op'>)</span>,
	unify_schemas <span class='op'>=</span> <span class='cn'>NULL</span>,
	<span class='va'>...</span>
	<span class='op'>)</span></pre>

	<h2 class="hasAnchor" id="arguments"><a class="anchor" href="#arguments"></a>Arguments</h2>
	<table class="ref-arguments">
	<colgroup><col class="name" /><col class="desc" /></colgroup>
	<tr>
	<th>sources</th>
	<td><p>One of:</p><ul>
	<li><p>a string path or URI to a directory containing data files</p></li>
	<li><p>a string path or URI to a single file</p></li>
	<li><p>a character vector of paths or URIs to individual data files</p></li>
	<li><p>a list of <code>Dataset</code> objects as created by this function</p></li>
	<li><p>a list of <code>DatasetFactory</code> objects as created by <code><a href='dataset_factory.html'>dataset_factory()</a></code>.</p></li>
	</ul>

	<p>When <code>sources</code> is a vector of file URIs, they must all use the same protocol
	and point to files located in the same file system and having the same
	format.</p></td>
	</tr>
	<tr>
	<th>schema</th>
	<td><p><a href='Schema.html'>Schema</a> for the <code>Dataset</code>. If <code>NULL</code> (the default), the schema
	will be inferred from the data sources.</p></td>
	</tr>
	<tr>
	<th>partitioning</th>
	<td><p>When <code>sources</code> is a directory path/URI, one of:</p><ul>
	<li><p>a <code>Schema</code>, in which case the file paths relative to <code>sources</code> will be
	parsed, and path segments will be matched with the schema fields. For
	example, <code><a href='Schema.html'>schema(year = int16(), month = int8())</a></code> would create partitions
	for file paths like <code>"2019/01/file.parquet"</code>, <code>"2019/02/file.parquet"</code>,
	etc.</p></li>
	<li><p>a character vector that defines the field names corresponding to those
	path segments (that is, you're providing the names that would correspond
	to a <code>Schema</code> but the types will be autodetected)</p></li>
	<li><p>a <code>HivePartitioning</code> or <code>HivePartitioningFactory</code>, as returned
	by <code><a href='hive_partition.html'>hive_partition()</a></code> which parses explicit or autodetected fields from
	Hive-style path segments</p></li>
	<li><p><code>NULL</code> for no partitioning</p></li>
	</ul>

	<p>The default is to autodetect Hive-style partitions. When <code>sources</code> is not a
	directory path/URI, <code>partitioning</code> is ignored.</p></td>
	</tr>
	<tr>
	<th>unify_schemas</th>
	<td><p>logical: should all data fragments (files, <code>Dataset</code>s)
	be scanned in order to create a unified schema from them? If <code>FALSE</code>, only
	the first fragment will be inspected for its schema. Use this fast path
	when you know and trust that all fragments have an identical schema.
	The default is <code>FALSE</code> when creating a dataset from a directory path/URI or
	vector of file paths/URIs (because there may be many files and scanning may
	be slow) but <code>TRUE</code> when <code>sources</code> is a list of <code>Dataset</code>s (because there
	should be few <code>Dataset</code>s in the list and their <code>Schema</code>s are already in
	memory).</p></td>
	</tr>
	<tr>
	<th>...</th>
	<td><p>additional arguments passed to <code><a href='dataset_factory.html'>dataset_factory()</a></code> when <code>sources</code>
	is a directory path/URI or vector of file paths/URIs, otherwise ignored.
	These may include <code>format</code> to indicate the file format, or other
	format-specific options.</p></td>
	</tr>
	</table>

	<h2 class="hasAnchor" id="value"><a class="anchor" href="#value"></a>Value</h2>

	<p>A <a href='Dataset.html'>Dataset</a> R6 object. Use <code>dplyr</code> methods on it to query the data,
	or call <code><a href='Scanner.html'>$NewScan()</a></code> to construct a query directly.</p>
	<h2 class="hasAnchor" id="see-also"><a class="anchor" href="#see-also"></a>See also</h2>

	<div class='dont-index'><p><code><a href='../articles/dataset.html'>vignette("dataset", package = "arrow")</a></code></p></div>

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