[R] help with loop
Wacek Kusnierczyk
Waclaw.Marcin.Kusnierczyk at idi.ntnu.no
Thu Mar 12 14:19:02 CET 2009
is your data a data frame or a matrix? do you want to compute the
differences columnwise, i.e., for each column independently? consider
this example:
# generate and display dummy data
(d = as.data.frame(replicate(3, sample(5))))
# compute successive differences columnwise
as.data.frame(apply(d, 2, diff))
apply(as.matrix(d), 2, diff)
see ?apply and ?diff for details. note that apply will return a matrix
both when given a data frame and when given a matrix.
vQ
Rafael Moral wrote:
> Dear useRs,
> I'm trying to write a loop to sum my data in the following way:
> (the second - the first) + (the third - the second) + (the fourth - the third) + ...
> for each column.
>
> So, I wrote something like this:
>
> c <- list()
> for(i in 1:ncol(mydata)) {
> for(j in 2:nrow(mydata)) {
> c[[i]] <- sum(yc[j,i] - yc[(j-1),i])
> }}}
>
> As for the columns it works pretty fine, but it only returns the last subtraction, however, I need the sum of all subtractions.
>
> Any ideas?
>
> Regards,
> Rafael.
>
>
> Veja quais são os assuntos do momento no Yahoo! +Buscados
>
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>
>
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