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<table width="100%" summary="page for colwise {plyr}"><tr><td>colwise {plyr}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Column-wise function.</h2>

<h3>Description</h3>

<p>Turn a function that operates on a vector into a function that operates
column-wise on a data.frame.
</p>

<h3>Usage</h3>

<pre>
colwise(.fun, .cols = true, ...)

catcolwise(.fun, ...)

numcolwise(.fun, ...)
</pre>

<h3>Arguments</h3>

<table summary="R argblock">
<tr valign="top"><td><code>.fun</code></td>
<td>
<p>function</p>
</td></tr>
<tr valign="top"><td><code>.cols</code></td>
<td>
<p>either a function that tests columns for inclusion, or a
quoted object giving which columns to process</p>
</td></tr>
<tr valign="top"><td><code>...</code></td>
<td>
<p>other arguments passed on to <code>.fun</code></p>
</td></tr>
</table>

<h3>Details</h3>

<p><code>catcolwise</code> and <code>numcolwise</code> provide version that only operate
on discrete and numeric variables respectively.
</p>

<h3>Examples</h3>

<pre>
# Count number of missing values
nmissing &lt;- function(x) sum(is.na(x))

# Apply to every column in a data frame
colwise(nmissing)(baseball)
# This syntax looks a little different.  It is shorthand for the
# the following:
f &lt;- colwise(nmissing)
f(baseball)

# This is particularly useful in conjunction with d*ply
ddply(baseball, .(year), colwise(nmissing))

# To operate only on specified columns, supply them as the second
# argument.  Many different forms are accepted.
ddply(baseball, .(year), colwise(nmissing, .(sb, cs, so)))
ddply(baseball, .(year), colwise(nmissing, c("sb", "cs", "so")))
ddply(baseball, .(year), colwise(nmissing, ~ sb + cs + so))

# Alternatively, you can specify a boolean function that determines
# whether or not a column should be included
ddply(baseball, .(year), colwise(nmissing, is.character))
ddply(baseball, .(year), colwise(nmissing, is.numeric))
ddply(baseball, .(year), colwise(nmissing, is.discrete))

# These last two cases are particularly common, so some shortcuts are
# provided:
ddply(baseball, .(year), numcolwise(nmissing))
ddply(baseball, .(year), catcolwise(nmissing))

# You can supply additional arguments to either colwise, or the function
# it generates:
numcolwise(mean)(baseball, na.rm = TRUE)
numcolwise(mean, na.rm = TRUE)(baseball)
</pre>

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