Best way to achieve alternation in R's version of grep?

Question

I'm trying to extract the indices of a large matrix on the basis of grepping two separate strings.

An example matrix might look like:

a=as.matrix(c("a","b","c"))
a=cbind(a,c("yes", "no", "maybe"))
rownames(a)=c("one", "two","three")
colnames(a)=c("letter", "status")

Both of these work:

grep("letter", colnames(a))
grep("status", colnames(a))

I'd like this to work, but it doesn't:

grep("letter"|"status", colnames(a))

Is the easiest way to collect both greps just concatenating them into a vector, or is there something we can do within the grep function?:

cols_to_get= c(grep("letter", colnames(a)), grep("status", colnames(a)))

does this help? http://stackoverflow.com/questions/33695462/r-filter-a-column-which-contains-several-keywords — rawr, Mar 30 '16 at 19:24
I think what @rawr is indicating is that this has already been asked before, and that in your case `grep("letter|status",colnames(a))` would work. — RHertel, Mar 30 '16 at 19:27

gwatson · Accepted Answer · 2016-03-31T14:06:36.827

3

Use proper regex? grep("letter|status", colnames(a))

edited Mar 31 '16 at 14:06

answered Mar 30 '16 at 19:32

gwatson

6

You don't need to use capture groups: `grep("letter|status", colnames(a))` – Jota Mar 30 '16 at 19:51

1 Answers1