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| <div class="page-header"> |
| <h1>Table class</h1> |
| <small class="dont-index">Source: <a href='https://github.com/apache/arrow/blob/master/r/R/table.R'><code>R/table.R</code></a></small> |
| <div class="hidden name"><code>Table.Rd</code></div> |
| </div> |
| |
| <div class="ref-description"> |
| <p>A Table is a sequence of <a href='ChunkedArray.html'>chunked arrays</a>. They |
| have a similar interface to <a href='RecordBatch.html'>record batches</a>, but they can be |
| composed from multiple record batches or chunked arrays.</p> |
| </div> |
| |
| |
| |
| <h2 class="hasAnchor" id="factory"><a class="anchor" href="#factory"></a>Factory</h2> |
| |
| |
| |
| |
| <p>The <code>Table$create()</code> function takes the following arguments:</p><ul> |
| <li><p><code>...</code> arrays, chunked arrays, or R vectors, with names; alternatively, |
| an unnamed series of <a href='RecordBatch.html'>record batches</a> may also be provided, |
| which will be stacked as rows in the table.</p></li> |
| <li><p><code>schema</code> a <a href='Schema.html'>Schema</a>, or <code>NULL</code> (the default) to infer the schema from |
| the data in <code>...</code></p></li> |
| </ul> |
| |
| <h2 class="hasAnchor" id="s-methods-and-usage"><a class="anchor" href="#s-methods-and-usage"></a>S3 Methods and Usage</h2> |
| |
| |
| |
| <p>Tables are data-frame-like, and many methods you expect to work on |
| a <code>data.frame</code> are implemented for <code>Table</code>. This includes <code><a href='https://rdrr.io/r/base/Extract.html'>[</a></code>, <code><a href='https://rdrr.io/r/base/Extract.html'>[[</a></code>, |
| <code><a href='https://rdrr.io/r/base/Extract.html'>$</a></code>, <code>names</code>, <code>dim</code>, <code>nrow</code>, <code>ncol</code>, <code>head</code>, and <code>tail</code>. You can also pull |
| the data from an Arrow table into R with <code><a href='https://rdrr.io/r/base/as.data.frame.html'>as.data.frame()</a></code>. See the |
| examples.</p> |
| <p>A caveat about the <code><a href='https://rdrr.io/r/base/Extract.html'>$</a></code> method: because <code>Table</code> is an <code>R6</code> object, |
| <code><a href='https://rdrr.io/r/base/Extract.html'>$</a></code> is also used to access the object's methods (see below). Methods take |
| precedence over the table's columns. So, <code>tab$Slice</code> would return the |
| "Slice" method function even if there were a column in the table called |
| "Slice".</p> |
| <h2 class="hasAnchor" id="r-methods"><a class="anchor" href="#r-methods"></a>R6 Methods</h2> |
| |
| |
| |
| <p>In addition to the more R-friendly S3 methods, a <code>Table</code> object has |
| the following R6 methods that map onto the underlying C++ methods:</p><ul> |
| <li><p><code>$column(i)</code>: Extract a <code>ChunkedArray</code> by integer position from the table</p></li> |
| <li><p><code>$ColumnNames()</code>: Get all column names (called by <code><a href='https://rdrr.io/r/base/names.html'>names(tab)</a></code>)</p></li> |
| <li><p><code>$RenameColumns(value)</code>: Set all column names (called by <code>names(tab) <- value</code>)</p></li> |
| <li><p><code>$GetColumnByName(name)</code>: Extract a <code>ChunkedArray</code> by string name</p></li> |
| <li><p><code>$field(i)</code>: Extract a <code>Field</code> from the table schema by integer position</p></li> |
| <li><p><code>$SelectColumns(indices)</code>: Return new <code>Table</code> with specified columns, expressed as 0-based integers.</p></li> |
| <li><p><code>$Slice(offset, length = NULL)</code>: Create a zero-copy view starting at the |
| indicated integer offset and going for the given length, or to the end |
| of the table if <code>NULL</code>, the default.</p></li> |
| <li><p><code>$Take(i)</code>: return an <code>Table</code> with rows at positions given by |
| integers <code>i</code>. If <code>i</code> is an Arrow <code>Array</code> or <code>ChunkedArray</code>, it will be |
| coerced to an R vector before taking.</p></li> |
| <li><p><code>$Filter(i, keep_na = TRUE)</code>: return an <code>Table</code> with rows at positions where logical |
| vector or Arrow boolean-type <code>(Chunked)Array</code> <code>i</code> is <code>TRUE</code>.</p></li> |
| <li><p><code>$SortIndices(names, descending = FALSE)</code>: return an <code>Array</code> of integer row |
| positions that can be used to rearrange the <code>Table</code> in ascending or descending |
| order by the first named column, breaking ties with further named columns. |
| <code>descending</code> can be a logical vector of length one or of the same length as |
| <code>names</code>.</p></li> |
| <li><p><code>$serialize(output_stream, ...)</code>: Write the table to the given |
| <a href='OutputStream.html'>OutputStream</a></p></li> |
| <li><p><code>$cast(target_schema, safe = TRUE, options = cast_options(safe))</code>: Alter |
| the schema of the record batch.</p></li> |
| </ul> |
| |
| <p>There are also some active bindings:</p><ul> |
| <li><p><code>$num_columns</code></p></li> |
| <li><p><code>$num_rows</code></p></li> |
| <li><p><code>$schema</code></p></li> |
| <li><p><code>$metadata</code>: Returns the key-value metadata of the <code>Schema</code> as a named list. |
| Modify or replace by assigning in (<code>tab$metadata <- new_metadata</code>). |
| All list elements are coerced to string. See <code><a href='Schema.html'>schema()</a></code> for more information.</p></li> |
| <li><p><code>$columns</code>: Returns a list of <code>ChunkedArray</code>s</p></li> |
| </ul> |
| |
| |
| <h2 class="hasAnchor" id="examples"><a class="anchor" href="#examples"></a>Examples</h2> |
| <pre class="examples"><div class='input'><span class='co'># \donttest{</span> |
| <span class='va'>tab</span> <span class='op'><-</span> <span class='va'>Table</span><span class='op'>$</span><span class='fu'>create</span><span class='op'>(</span>name <span class='op'>=</span> <span class='fu'><a href='https://rdrr.io/r/base/colnames.html'>rownames</a></span><span class='op'>(</span><span class='va'>mtcars</span><span class='op'>)</span>, <span class='va'>mtcars</span><span class='op'>)</span> |
| <span class='fu'><a href='https://rdrr.io/r/base/dim.html'>dim</a></span><span class='op'>(</span><span class='va'>tab</span><span class='op'>)</span> |
| </div><div class='output co'>#> [1] 32 12</div><div class='input'><span class='fu'><a href='https://rdrr.io/r/base/dim.html'>dim</a></span><span class='op'>(</span><span class='fu'><a href='https://rdrr.io/r/utils/head.html'>head</a></span><span class='op'>(</span><span class='va'>tab</span><span class='op'>)</span><span class='op'>)</span> |
| </div><div class='output co'>#> [1] 6 12</div><div class='input'><span class='fu'><a href='https://rdrr.io/r/base/names.html'>names</a></span><span class='op'>(</span><span class='va'>tab</span><span class='op'>)</span> |
| </div><div class='output co'>#> [1] "name" "mpg" "cyl" "disp" "hp" "drat" "wt" "qsec" "vs" "am" |
| #> [11] "gear" "carb"</div><div class='input'><span class='va'>tab</span><span class='op'>$</span><span class='va'>mpg</span> |
| </div><div class='output co'>#> ChunkedArray |
| #> [ |
| #> [ |
| #> 21, |
| #> 21, |
| #> 22.8, |
| #> 21.4, |
| #> 18.7, |
| #> 18.1, |
| #> 14.3, |
| #> 24.4, |
| #> 22.8, |
| #> 19.2, |
| #> ... |
| #> 15.2, |
| #> 13.3, |
| #> 19.2, |
| #> 27.3, |
| #> 26, |
| #> 30.4, |
| #> 15.8, |
| #> 19.7, |
| #> 15, |
| #> 21.4 |
| #> ] |
| #> ]</div><div class='input'><span class='va'>tab</span><span class='op'>[[</span><span class='st'>"cyl"</span><span class='op'>]</span><span class='op'>]</span> |
| </div><div class='output co'>#> ChunkedArray |
| #> [ |
| #> [ |
| #> 6, |
| #> 6, |
| #> 4, |
| #> 6, |
| #> 8, |
| #> 6, |
| #> 8, |
| #> 4, |
| #> 4, |
| #> 6, |
| #> ... |
| #> 8, |
| #> 8, |
| #> 8, |
| #> 4, |
| #> 4, |
| #> 4, |
| #> 8, |
| #> 6, |
| #> 8, |
| #> 4 |
| #> ] |
| #> ]</div><div class='input'><span class='fu'><a href='https://rdrr.io/r/base/as.data.frame.html'>as.data.frame</a></span><span class='op'>(</span><span class='va'>tab</span><span class='op'>[</span><span class='fl'>4</span><span class='op'>:</span><span class='fl'>8</span>, <span class='fu'><a href='https://rdrr.io/r/base/c.html'>c</a></span><span class='op'>(</span><span class='st'>"gear"</span>, <span class='st'>"hp"</span>, <span class='st'>"wt"</span><span class='op'>)</span><span class='op'>]</span><span class='op'>)</span> |
| </div><div class='output co'>#> <span style='color: #949494;'># A tibble: 5 x 3</span> |
| #> gear hp wt |
| #> <span style='color: #949494; font-style: italic;'><dbl></span> <span style='color: #949494; font-style: italic;'><dbl></span> <span style='color: #949494; font-style: italic;'><dbl></span> |
| #> <span style='color: #BCBCBC;'>1</span> 3 110 3.22 |
| #> <span style='color: #BCBCBC;'>2</span> 3 175 3.44 |
| #> <span style='color: #BCBCBC;'>3</span> 3 105 3.46 |
| #> <span style='color: #BCBCBC;'>4</span> 3 245 3.57 |
| #> <span style='color: #BCBCBC;'>5</span> 4 62 3.19</div><div class='input'><span class='co'># }</span> |
| </div></pre> |
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