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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><title>R: Split array, apply function, and return results in a list.</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="stylesheet" type="text/css" href="R.css" /> </head><body> <table width="100%" summary="page for alply {plyr}"><tr><td>alply {plyr}</td><td style="text-align: right;">R Documentation</td></tr></table> <h2>Split array, apply function, and return results in a list.</h2> <h3>Description</h3> <p>For each slice of an array, apply function then combine results into a list. </p> <h3>Usage</h3> <pre> alply( .data, .margins, .fun = NULL, ..., .expand = TRUE, .progress = "none", .inform = FALSE, .parallel = FALSE, .paropts = NULL, .dims = FALSE ) </pre> <h3>Arguments</h3> <table summary="R argblock"> <tr valign="top"><td><code>.data</code></td> <td> <p>matrix, array or data frame to be processed</p> </td></tr> <tr valign="top"><td><code>.margins</code></td> <td> <p>a vector giving the subscripts to split up <code>data</code> by. 1 splits up by rows, 2 by columns and c(1,2) by rows and columns, and so on for higher dimensions</p> </td></tr> <tr valign="top"><td><code>.fun</code></td> <td> <p>function to apply to each piece</p> </td></tr> <tr valign="top"><td><code>...</code></td> <td> <p>other arguments passed on to <code>.fun</code></p> </td></tr> <tr valign="top"><td><code>.expand</code></td> <td> <p>if <code>.data</code> is a data frame, should output be 1d (expand = FALSE), with an element for each row; or nd (expand = TRUE), with a dimension for each variable.</p> </td></tr> <tr valign="top"><td><code>.progress</code></td> <td> <p>name of the progress bar to use, see <code><a href="create_progress_bar.html">create_progress_bar</a></code></p> </td></tr> <tr valign="top"><td><code>.inform</code></td> <td> <p>produce informative error messages? This is turned off by default because it substantially slows processing speed, but is very useful for debugging</p> </td></tr> <tr valign="top"><td><code>.parallel</code></td> <td> <p>if <code>TRUE</code>, apply function in parallel, using parallel backend provided by foreach</p> </td></tr> <tr valign="top"><td><code>.paropts</code></td> <td> <p>a list of additional options passed into the <code><a href="../../foreach/html/foreach.html">foreach</a></code> function when parallel computation is enabled. This is important if (for example) your code relies on external data or packages: use the <code>.export</code> and <code>.packages</code> arguments to supply them so that all cluster nodes have the correct environment set up for computing.</p> </td></tr> <tr valign="top"><td><code>.dims</code></td> <td> <p>if <code>TRUE</code>, copy over dimensions and names from input.</p> </td></tr> </table> <h3>Details</h3> <p>The list will have "dims" and "dimnames" corresponding to the margins given. For instance <code>alply(x, c(3,2), ...)</code> where <code>x</code> has dims <code>c(4,3,2)</code> will give a result with dims <code>c(2,3)</code>. </p> <p><code>alply</code> is somewhat similar to <code><a href="../../base/html/apply.html">apply</a></code> for cases where the results are not atomic. </p> <h3>Value</h3> <p>list of results </p> <h3>Input</h3> <p>This function splits matrices, arrays and data frames by dimensions </p> <h3>Output</h3> <p>If there are no results, then this function will return a list of length 0 (<code>list()</code>). </p> <h3>References</h3> <p>Hadley Wickham (2011). The Split-Apply-Combine Strategy for Data Analysis. Journal of Statistical Software, 40(1), 1-29. <a href="https://www.jstatsoft.org/v40/i01/">https://www.jstatsoft.org/v40/i01/</a>. </p> <h3>See Also</h3> <p>Other array input: <code><a href="a_ply.html">a_ply</a>()</code>, <code><a href="aaply.html">aaply</a>()</code>, <code><a href="adply.html">adply</a>()</code> </p> <p>Other list output: <code><a href="dlply.html">dlply</a>()</code>, <code><a href="llply.html">llply</a>()</code>, <code><a href="mlply.html">mlply</a>()</code> </p> <h3>Examples</h3> <pre> alply(ozone, 3, quantile) alply(ozone, 3, function(x) table(round(x))) </pre> <hr /><div style="text-align: center;">[Package <em>plyr</em> version 1.8.7 <a href="00Index.html">Index</a>]</div> </body></html>