CODEWITHSUNDEEP
rvectorfindmatch
Ash
Ash

Reputation: 350

R to find elements in a vector that their indices dose not exist in another vector

I have a vector like the following:

VEC = c(4,8,8,8)

I also have an indices vector which tells me what elements in VEC I should ignore:

indx = c(2,4)

I want to get the index of the first element whos value is 8 but the index does not exist in indx array. how can I do that?

So basically i should get 3 as the answer. VEC[3] = 8 (but the second 8 not the first one).

Here is another one VEC = c(1,3,5,3,3,3,3) and here is the ignore list: indx=c(1,2,4,6) Let's say I'm looking for values that match 3. The index that should be return is 5 because VEC[1], VEC[2], VEC[4], VEC[6] are in the ignore list and the first occurrence has index value of 5.

Upvotes: 0

Views: 718

Answers (2)

teucer
teucer

Reputation: 6238

That might be more efficient

VEC <- c(4,8,8,8)
indx <- c(2,4)

VEC[indx] <- NA
which(VEC==8)[1]

Upvotes: 3

MrFlick
MrFlick

Reputation: 206177

If you want the original index, then you can do something like

VEC <- c(4,8,8,8)
indx <- c(2,4)

which(VEC==8 & !(seq_along(VEC) %in% indx))
which(VEC==8 & !(seq_along(VEC) %in% indx))[1] #to get just the first

This is a bit ugly but might be more efficient

ok<-`[<-`(!logical(length(VEC)), indx, FALSE)
which(VEC==8 & ok)
which(VEC==8 & ok)[1] #to get just the first

Upvotes: 4

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