2

I tried to do this:

DT <- data.table(Monthname = month.name, id = 1:3, a = abs(rnorm(12)), b = abs(rnorm(12)), c = abs(rnorm(12)), d = abs(rnorm(12)))
setkey(DT, id)
ANS <- DT[,lapply(.SD, mean)/lapply(.SD, sd), by = 'id', .SDcols = names(DT)[-1]]

but it gives error. So, Are there any ways to do this ? Thank You.

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  • An alternative to the answer below is to define a function like myfun <- function(x) mean(x)/sd(x) and then use DT[, lapply(.SD, myfun), by = "id", .SDcols = names(DT)[-1]]. Commented Feb 17, 2014 at 16:15

1 Answer 1

Reset to default
2

Just that same as one would use lapply in other contexts:

ANS <- DT[,lapply(.SD, function(x) mean(x)/sd(x) ), by = 'id', .SDcols = names(DT)[-1]]
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