当R中的另一个向量为TRUE时，保留向量中的值

Question

I have got two vectors, both with dimensions 30000x1, so only one column and many rows. First vector contains values, second only TRUE or FALSE.

I want to keep all the rows of vector1 where at the same row vector2 equals TRUE.

I have tried combinations like:

res=apply(vector1,2,vector2)
res=vector1(vector2)
res=vector1[vector2]

but I can't figure this out. Thanks a lot for help.

Example:

vector1:

123
345
667

vector2:
TRUE
FALSE
TRUE

res:
123
667

Answer 1

In R you can index into one vector using a second vector of the same length that contains Boolean values, such that wherever the second vector contains TRUE you select the corresponding element of the first.

So your third way works for me

v1=c(123,345,667)
v2=c(TRUE,FALSE,TRUE)
v1[v2]

which outputs

[1] 123 667

This is because v2 contains TRUE at positions 1 and 3, and so v1[v2] is equivalent to v1[c(1,3)] .

See the point 1 of the introductory documentation on indexing. Specifically

[indexing with] a logical vector. In this case the index vector must be of the same length as the vector from which elements are to be selected. Values corresponding to TRUE in the index vector are selected and those corresponding to FALSE are omitted

Answer 2

This works:

 x= 1:3
 y = c(T,F,T)
 x
 #[1] 1 2 3
 y
 #[1]  TRUE FALSE  TRUE
 x[y]
 #[1] 1 3