From: jim holtman <jholtman_at_gmail.com>

Date: Mon, 10 Dec 2007 15:46:06 -0800

Date: Mon, 10 Dec 2007 15:46:06 -0800

?ifelse

*> a<-rep(c("A","B"),50)
**> b<-rep(1,100)
**> c<-rep(2,100)
*

> d <- ifelse(a == "A", b, c)

*> head(d)
*

[1] 1 2 1 2 1 2

On Dec 10, 2007 3:41 PM, Neil Stewart <neil.stewart_at_warwick.ac.uk> wrote:

> I would like to make a new vector with values taken from two existing

*> vectors conditional upon a third. At present I am doing this with a for loop
**> but wonder if there is not a neater way, given some of the very neat things
**> R can do.
**>
**> a<-rep(c("A","B"),50)
**> b<-rep(1,100)
**> c<-rep(2,100)
**>
**> a is thus "A" "B" "A" "B" "A" "B"...
**> b is thus 1 1 1 1 1 1 ...
**> c is thus 2 2 2 2 2 2 ...
**>
**> I want d[i] to be b[i] if a[i]=="A" and c[i] if a[i]=="B". I'm current using
**> a for loop:
**>
**> d<-rep(0,100) # initialise d
**> for(i in 1:length(a)) {if(a[i]=="A") d[i]<-b[i] else d[i]<-c[i]}
**>
**> d is thus 1 2 1 2 1 2 1 2 1 ...
**>
**> Is it possible to do something simpler, say along the lines of the c-style
**> ?: conditional statement, or at least avoiding the for loop.
**>
**> d <- a=="A"?b:c # doesn't work, but you get the idea
**>
**> Thanks in advance,
**> Neil
**>
**> ______________________________________________
**> 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.
**>
*

-- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem you are trying to solve? ______________________________________________ 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.Received on Tue 11 Dec 2007 - 00:04:11 GMT

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