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| <div class="page-header"> |
| <h1>ParquetFileReader class</h1> |
| <small class="dont-index">Source: <a href='https://github.com/apache/arrow/blob/master/r/R/parquet.R'><code>R/parquet.R</code></a></small> |
| <div class="hidden name"><code>ParquetFileReader.Rd</code></div> |
| </div> |
| |
| <div class="ref-description"> |
| <p>This class enables you to interact with Parquet files.</p> |
| </div> |
| |
| |
| |
| <h2 class="hasAnchor" id="factory"><a class="anchor" href="#factory"></a>Factory</h2> |
| |
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| |
| <p>The <code>ParquetFileReader$create()</code> factory method instantiates the object and |
| takes the following arguments:</p><ul> |
| <li><p><code>file</code> A character file name, raw vector, or Arrow file connection object |
| (e.g. <code>RandomAccessFile</code>).</p></li> |
| <li><p><code>props</code> Optional <a href='ParquetArrowReaderProperties.html'>ParquetArrowReaderProperties</a></p></li> |
| <li><p><code>mmap</code> Logical: whether to memory-map the file (default <code>TRUE</code>)</p></li> |
| <li><p><code>...</code> Additional arguments, currently ignored</p></li> |
| </ul> |
| |
| <h2 class="hasAnchor" id="methods"><a class="anchor" href="#methods"></a>Methods</h2> |
| |
| |
| |
| <ul> |
| <li><p><code>$ReadTable(column_indices)</code>: get an <code><a href='Table.html'>arrow::Table</a></code> from the file. The optional |
| <code>column_indices=</code> argument is a 0-based integer vector indicating which columns to retain.</p></li> |
| <li><p><code>$ReadRowGroup(i, column_indices)</code>: get an <code><a href='Table.html'>arrow::Table</a></code> by reading the <code>i</code>th row group (0-based). |
| The optional <code>column_indices=</code> argument is a 0-based integer vector indicating which columns to retain.</p></li> |
| <li><p><code>$ReadRowGroups(row_groups, column_indices)</code>: get an <code><a href='Table.html'>arrow::Table</a></code> by reading several row groups (0-based integers). |
| The optional <code>column_indices=</code> argument is a 0-based integer vector indicating which columns to retain.</p></li> |
| <li><p><code>$GetSchema()</code>: get the <code><a href='Schema.html'>arrow::Schema</a></code> of the data in the file</p></li> |
| <li><p><code>$ReadColumn(i)</code>: read the <code>i</code>th column (0-based) as a <a href='ChunkedArray.html'>ChunkedArray</a>.</p></li> |
| </ul> |
| |
| <h2 class="hasAnchor" id="active-bindings"><a class="anchor" href="#active-bindings"></a>Active bindings</h2> |
| |
| |
| |
| <ul> |
| <li><p><code>$num_rows</code>: number of rows.</p></li> |
| <li><p><code>$num_columns</code>: number of columns.</p></li> |
| <li><p><code>$num_row_groups</code>: number of row groups.</p></li> |
| </ul> |
| |
| |
| <h2 class="hasAnchor" id="examples"><a class="anchor" href="#examples"></a>Examples</h2> |
| <pre class="examples"><div class='input'><span class='kw'>if</span> <span class='op'>(</span><span class='cn'>FALSE</span><span class='op'>)</span> <span class='op'>{</span> |
| <span class='va'>f</span> <span class='op'><-</span> <span class='fu'><a href='https://rdrr.io/r/base/system.file.html'>system.file</a></span><span class='op'>(</span><span class='st'>"v0.7.1.parquet"</span>, package<span class='op'>=</span><span class='st'>"arrow"</span><span class='op'>)</span> |
| <span class='va'>pq</span> <span class='op'><-</span> <span class='va'>ParquetFileReader</span><span class='op'>$</span><span class='fu'>create</span><span class='op'>(</span><span class='va'>f</span><span class='op'>)</span> |
| <span class='va'>pq</span><span class='op'>$</span><span class='fu'>GetSchema</span><span class='op'>(</span><span class='op'>)</span> |
| <span class='kw'>if</span> <span class='op'>(</span><span class='fu'><a href='codec_is_available.html'>codec_is_available</a></span><span class='op'>(</span><span class='st'>"snappy"</span><span class='op'>)</span><span class='op'>)</span> <span class='op'>{</span> |
| <span class='co'># This file has compressed data columns</span> |
| <span class='va'>tab</span> <span class='op'><-</span> <span class='va'>pq</span><span class='op'>$</span><span class='fu'>ReadTable</span><span class='op'>(</span><span class='op'>)</span> |
| <span class='va'>tab</span><span class='op'>$</span><span class='va'>schema</span> |
| <span class='op'>}</span> |
| <span class='op'>}</span> |
| </div></pre> |
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