How to 'subset' a named vector in R?

Question

Suppose I have this named vector in R:

foo=vector()
foo['a']=1
foo['b']=2
foo['c']=3

How do I most cleanly make another named vector with only elements 'a' and 'c'?

If this were a data frame with a column "name" and a column "value" I could use

subset(df, name %in% c('a', 'b'))

which is nice because subset can evaluate any boolean expression, so it is quite flexible.

You can still use `subset(foo, names(foo) %in% c('a', 'c'))` but @AndreyShabalin answer is cleaner — dickoa, Dec 27 '13 at 04:24
Additionally take a look at this question: [In R, why is `[` better than `subset`?](http://stackoverflow.com/questions/9860090/in-r-why-is-better-than-subset) — Scott Ritchie, Dec 27 '13 at 04:39

score 15 · Accepted Answer · answered Dec 27 '13 at 04:20

15

How about this:

foo[c('a','b')]

answered Dec 27 '13 at 04:20

Andrey Shabalin

Is there a way to negate this syntax? It seems that you can write `foo[-1]` but not `foo[-"a"]`. – Dan Chaltiel Oct 08 '21 at 15:59
1

`foo[!(names(foo) %in% c('a','b'))]` – Andrey Shabalin Oct 08 '21 at 17:44

score 3 · Answer 2 · answered Dec 27 '13 at 04:24

3

As a sidenote, avoid 'growing' structures in R. Your example can be write like this also:

foo = c(a = 1, b = 2, c = 3)

To subset just do like Andrey's answer:

foo[c('a','b')]

answered Dec 27 '13 at 04:24

Fernando

2 Answers2