R: Loop over Variables in a Data Frame or Environment
foreach
R Documentation
Loop over Variables in a Data Frame or Environment
Description
foreach evaluates an expression given as second argument by substituting
in variables. The expression may also contain assignments, which take effect in
the callers environment.
Usage
foreach(...)
Arguments
...
tagged and untagged arguments.
The tagged arguments define the 'variables' that are looped over,
the first untagged argument defines the expression wich is
evaluated.
Examples
x <- 1:3
y <- -(1:3)
z <- c("Uri","Schwyz","Unterwalden")
print(x)
print(y)
print(z)
foreach(var=c(x,y,z), # assigns names
names(var) <- letters[1:3] # to the elements of x, y, and z
)
print(x)
print(y)
print(z)
ds <- data.set(
a = c(1,2,3,2,3,8,9),
b = c(2,8,3,2,1,8,9),
c = c(1,3,2,1,2,8,8)
)
print(ds)
ds <- within(ds,{
description(a) <- "First item in questionnaire"
description(b) <- "Second item in questionnaire"
description(c) <- "Third item in questionnaire"
wording(a) <- "What number do you like first?"
wording(b) <- "What number do you like second?"
wording(c) <- "What number do you like third?"
foreach(x=c(a,b,c),{ # Lazy data documentation:
labels(x) <- c( # a,b,c get value labels in one statement
one = 1,
two = 2,
three = 3,
"don't know" = 8,
"refused to answer" = 9)
missing.values(x) <- c(8,9)
})
})
as.data.frame(ds)
ds <- within(ds,foreach(x=c(a,b,c),{
measurement(x) <- "interval"
}))
as.data.frame(ds)