As above, with
returns the value of the last evaluated expression. It is handy for one-liners such as:
with(cars, summary(lm (speed ~ dist)))
but is not suitable for sending multiple expressions.
I often find within
useful for manipulating a data.frame
or list
(or data.table
) as I find the syntax easy to read.
I feel that the documentation could be improved by adding examples of use in this regard, e.g.:
df1 <- data.frame(a=1:3,
b=4:6,
c=letters[1:3])
## library("data.table")
## df1 <- as.data.table(df1)
df1 <- within(df1, {
a <- 10:12
b[1:2] <- letters[25:26]
c <- a
})
df1
giving
a b c
1: 10 y 10
2: 11 z 11
3: 12 6 12
and
df1 <- as.list(df1)
df1 <- within(df1, {
a <- 20:23
b[1:2] <- letters[25:26]
c <- paste0(a, b)
})
df1
giving
$a
[1] 20 21 22 23
$b
[1] "y" "z" "6"
$c
[1] "20y" "21z" "226" "23y"
Note also that methods("within")
gives only these object types, being:
within.data.frame
within.list
- (and
within.data.table
if the package is loaded).
Other packages may define additional methods.
Perhaps unexpectedly for some, with
and within
are generally not appropriate choices when manipulating variables within defined environments...
To address the comment - there is no within.environment
method. Using with
requires you to have the function you're calling within the environment, which somewhat defeats the purpose for me e.g.
df1 <- as.environment(df1)
## with(df1, ls()) ## Error
assign("ls", ls, envir=df1)
with(df1, ls())