问题
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.
回答1:
setdiff(v1, v2)
# [1] 1 3 5 6 8 9 10
回答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.
来源：https://stackoverflow.com/questions/16298153/which-numbers-are-present-in-a-vector-but-not-in-another-one