On 25/01/12 05:14, Francisco wrote:
Hello,
I have a dataset with 40 variables, some of them are always 0 (each
row). I would like to make a subset containing only the columns which
values are not all 0, but I don't know how to do it.
I tried:
for(cut_column in 1:40) {
if(sum(dataset[,cut_column])!=0) {
columns_useful<-c(columns_useful,dataset[cut_column])
}
}
sorted_dataset<-subset(dataset, select=columns_useful)
But it doesn't work.
Try:
good_dataset <- dataset[,sapply(dataset,function(x){!all(x==0)})]
This works modulo possible gotchas induced by floating point arithmetic.
Another possibility:
tol <- sqrt(.Machine$double.eps)
good_dataset <-
dataset[,sapply(dataset,function(x){!all(abs(x)<=tol)})]
Or:
good_dataset <-
dataset[,sapply(dataset,function(x){!isTRUE(all.equal(x,rep(0,length(x))))})]
The foregoing could trip up if some columns of "dataset" have extra
attributes tagging
along. E.g. the column could actually be a numeric matrix of zeroes ---
in which case
it wouldn't get dropped.
cheers,
Rolf Turner
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