R help - Oct 2011 - 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

How about a trick?
> b <- as.numeric(factor(b, levels=a))
> b
[1] 4 5 2 3 1 5 5 1


On Wed, Oct 19, 2011 at 5:38 PM, David Epstein <davideps at umich.edu>
wrote:
> 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
>
-- 
Sarah Goslee
http://www.functionaldiversity.org

> 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
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

thank you! that is straight forward.

On Wed, 2011-10-19 at 22:37 +0000, William Dunlap wrote:
> > match(b, a)
> [1] 4 5 2 3 1 5 5 1