How to get a variable's name based on its value

Question

If I have a list of interger, and I gave them string names, how do i get the name based on the value?

Is that possible?

Thanks

A [reproducible example](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) would make your question more precise and easier to verify potential answers. — MrFlick, May 08 '15 at 15:56

score 4 · Accepted Answer · edited May 08 '15 at 16:02

4

x <- list(a=2L,b=3L) 
names(x[which(x==2)])

edited May 08 '15 at 16:02

Frank

answered May 08 '15 at 15:49

Shenglin Chen

score 1 · Answer 2 · answered May 08 '15 at 15:38

match with names works:

x <- list(a=2L,b=3L)

names(x)[match(2L,x)]
# [1] "a"

This also works if x is not actually a list, but a vector: x <- c(a=2L,b=3L).

If the value is not unique, it selects the first match:

x <- list(a=2L,b=3L,d=2L)
names(x)[match(2L,x)] # still "a"

2 Answers2