Which numbers are present in a vector but not in a

Question

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• How to tell what is in one vector and not another? 5 answers

I guess it is a very easy question.

v1 = 1:10
v2 = c(2,4,7)

(none of the numbers are repeated. No need to use unique())

I want a vector containing all the values in v1 that are not in v2.

solution = c(1,3,5,6,8,9,10)

I can do this using a for loop but I'm sure there are easier solution.

Answer 1

setdiff(v1, v2)
# [1]  1  3  5  6  8  9 10

Answer 2

Use the %in% operator with logical NOT ( ! ) to subset v1 by values not in v2:

v1[ ! v1 %in% v2 ]
#[1]  1  3  5  6  8  9 10

Or you could look for non-matches of v1 in v2 (this is almost the same):

v1[ is.na( match( v1 , v2 ) ) ]
#[1]  1  3  5  6  8  9 10

Or using which to get the indices:

v1[  which( ! v1 %in% v2 ) ]
#[1]  1  3  5  6  8  9 10

All flavours of the same thing. And there are many more ways to do this. Definitely don't use a loop for this because this kind of operation is a perfect example of how you can take advatage of R's vectorisation. Loops are better to be called for their side-effects and/or when the processing to number of iterations ratio is large.