[R] Wildcard for indexing?

R. Michael Weylandt michael.weylandt at gmail.com
Tue Feb 14 15:59:39 CET 2012

I think the grep()-family (regular expressions) will be the easiest
way to do this, though it sounds like you might prefer grepl() which
returns a logical vector:

^[AB] # Starts with either an A or a B
^A_ # Starting with A_

a <-  c("A_A","A_B","C_A","BB","A_Asd"
grepl("^[AB]", a)


On Tue, Feb 14, 2012 at 9:54 AM, Johannes Radinger <JRadinger at gmx.at> 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
> /johannes
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