What does the dplyr period character "." reference?
<p>What does the period <code>.</code> reference in the following dplyr code?:</p>

<pre><code>(df &lt;- as.data.frame(matrix(rep(1:5, 5), ncol=5)))
#    V1 V2 V3 V4 V5
#  1  1  1  1  1  1
#  2  2  2  2  2  2
#  3  3  3  3  3  3
#  4  4  4  4  4  4
#  5  5  5  5  5  5

dplyr::mutate_each(df, funs(. == 5))
#       V1    V2    V3    V4    V5
#  1 FALSE FALSE FALSE FALSE FALSE
#  2 FALSE FALSE FALSE FALSE FALSE
#  3 FALSE FALSE FALSE FALSE FALSE
#  4 FALSE FALSE FALSE FALSE FALSE
#  5  TRUE  TRUE  TRUE  TRUE  TRUE
</code></pre>

<p>Is this shorthand for "all columns"? Is this <code>.</code> specific dplyr syntax or is it general R syntax (as discussed <a href="https://stackoverflow.com/questions/6951090/what-does-the-period-mean-in-the-following-r-excerpt">here</a>)?</p>

<p>Also, why does the following code result in an error?</p>

<pre><code>dplyr::filter(df, . == 5)
#  Error: object '.' not found
</code></pre>