How to save results into a empty vector in R?

Question

I have problem to create a empty vector in R, and save the results of another vector into them. This is my code:

k<-vector(mode = "numeric", length = 0)
for (j in length(Pe)){
  if ((Pe[j])>0) {
    k[j]<-Pe[j]
  }
}

The lenght of the vector Pe is 1000. I need only to save the values mayor than zero in the vector k, but when I type the vector k the display window show:

numerical(0)

This is the correct way to initiate a empty vector in R (k)?

Thanks

Answer 1

in fact, it can be much more easy. Type

 k <- c()

instead. But I think this won't get you what you want.

What happens when element p is not > 0? R will fill k[p] with NA, while I think you want k to be a shorter vector of only the elements of Pe which are > 0, not to be the same length but with NA's?

If so, you don't even need a loop. Try

k <- Pe[Pe > 0]

This will get you a vector only containing the elements of Pe > 0, no NA's.

Excuse my bad english, hope I helped you

Answer 2

As MaxPD pointed out

for (j in length(Pe)) print(j)

would only print the length of Pe, you should

for (j in seq_len(length(Pe))) print(j)
## or
for (j in seq_along(Pe)) print(j)
## or
for (j in 1:length(Pe)) print(j)

but in your case i wouldn't even use a loop

k<-vector(mode = "numeric", length = 0)
k[Pe > 0] <- Pe[Pe > 0]

should do the trick if both objects are vectors and have the same length.