[R] replacing values in one vector with corresponding index from another vector

[William Dunlap]

> match(b, a)
[1] 4 5 2 3 1 5 5 1

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of David Epstein
> Sent: Wednesday, October 19, 2011 2:39 PM
> To: r-help at r-project.org
> Subject: [R] replacing values in one vector with corresponding index from another vector
> 
> A quick question for the gurus...
> 
> Given:
> 
> a=c(58,73,100,40,70)
> b=c(40,70,73,100,58,70,70,58)
> 
> How can I replace the elements of "b" with the corresponding index
> numbers from "a" that start at 1? All values in "a" are unique. So, I
> end up with:
> 
> b=c(4,5,2,3,1,5,5,1)
> 
> I believe I need to use one of the "apply" functions in combination with
> "which" but I cannot make it work.
> 
> thank you,
> -david
> 
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