Loop over Variables in a Data Frame or Environment
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.
foreach(...)
... |
tagged and untagged arguments. The tagged arguments define the 'variables' that are looped over, the first untagged argument defines the expression wich is evaluated. |
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)
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