[R] Wildcard for indexing?

[Duncan Murdoch]

On 14/02/2012 9:54 AM, Johannes Radinger wrote:
> Hi,
>
> I'd like to know if it is possible to use wildcards * for indexing...
> E.g. I have a vector of strings. Now I'd like to select all elements
> which start with A_*? I'd also need to combine that with logical operators:
>
> "Select all elements of a vector that start with A (A*) OR that start with B (B*)"
>
> Probably that is quite easy. I looked into grep() which I think might perform such tasks, but probably there is a more straigth forward solution.
>
> a<- c("A_A","A_B","C_A","BB","A_Asd")
> a[a=="A_A"| a=="A_B"] # here I'd like an index but with wildcard

Try grepl():

a[grepl("^[AB]", a)]

is probably the simplest way for your example.

Duncan Murdoch