Quote variables to create a list of unevaluated expressions for later evaluation.
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))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.