. {plyr} | R Documentation |
This function is similar to ~
in that it is
used to capture the name of variables, not their current
value. This is used throughout plyr to specify the names
of variables (or more complicated expressions).
.(..., .env = parent.frame())
... |
unevaluated expressions to be recorded. Specify names if you want the set the names of the resultant variables |
.env |
environment in which unbound symbols in
|
Similar tricks can be performed with
substitute
, but when functions can be
called in multiple ways it becomes increasingly tricky to
ensure that the values are extracted from the correct
frame. Substitute tricks also make it difficult to
program against the functions that use them, while the
quoted
class provides as.quoted.character
to convert strings to the appropriate data structure.
list of symbol and language primitives
.(a, b, c) .(first = a, second = b, third = c) .(a ^ 2, b - d, log(c)) as.quoted(~ a + b + c) as.quoted(a ~ b + c) as.quoted(c("a", "b", "c")) # Some examples using ddply - look at the column names ddply(mtcars, "cyl", each(nrow, ncol)) ddply(mtcars, ~ cyl, each(nrow, ncol)) ddply(mtcars, .(cyl), each(nrow, ncol)) ddply(mtcars, .(log(cyl)), each(nrow, ncol)) ddply(mtcars, .(logcyl = log(cyl)), each(nrow, ncol)) ddply(mtcars, .(vs + am), each(nrow, ncol)) ddply(mtcars, .(vsam = vs + am), each(nrow, ncol))