[R] Finding elements in a character vector

Phil Spector spector at stat.berkeley.edu
Sat Apr 9 02:03:26 CEST 2011


 					- Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu

On Fri, 8 Apr 2011, Downey, Patrick wrote:

> Hello,
> I have two character vectors: list.a and list.b. Every element of list.a
> appears somewhere in list.b. Not all elements of list.b are in list.a, and
> some elements of list.b appear multiple times in list.a. I want to create a
> new vector (index) of the same length as list.a where the nth element of
> index is the location in list.b of the nth element of list.a.
> This code will work, but I have heard over and over again that using loops
> is inefficient in R and that there are (almost always) better ways to do
> things.
> for(i in 1:length(list.a)){
> index[i] <- seq(1,length(list.b))[list.b==list.a[i]]
> }
> Thank you,
> Mitch
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