# [R] Is there a neat R trick for this?

Bert Gunter gunter.berton at gene.com
Tue Feb 12 20:11:44 CET 2013

```Take a look at:

>get("%in%")

to see why this (i.e. which(y %in% x) ) is not a good idea.

-- Bert

On Tue, Feb 12, 2013 at 9:48 AM, Nordlund, Dan (DSHS/RDA)
<NordlDJ at dshs.wa.gov> wrote:
> Another option is
>
> which(y %in% x)
>
>
> Dan
>
> Daniel J. Nordlund
> Washington State Department of Social and Health Services
> Planning, Performance, and Accountability
> Research and Data Analysis Division
> Olympia, WA 98504-5204
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>> project.org] On Behalf Of Pascal Oettli
>> Sent: Tuesday, February 12, 2013 2:21 AM
>> To: Robert Latest
>> Cc: r-help at r-project.org
>> Subject: Re: [R] Is there a neat R trick for this?
>>
>> Hello,
>>
>> ?match
>>
>>  > x <- c(4,5,6)
>>  > y <- c(10,1,5,12,4,13,14)
>>  > match(x,y)
>> [1]  5  3 NA
>>
>> Hope this helps,
>> Pascal
>>
>>
>> Le 12/02/2013 19:09, Robert Latest a écrit :
>> > Hello all,
>> >
>> > given two vectors X and Y I'd like to receive a vector Z which
>> > contains, for each element of X, the index of the corresponding
>> > element in Y (or NA if that element isn't in Y).
>> >
>> > Example:
>> >
>> > x <- c(4,5,6)
>> > y <- c(10,1,5,12,4,13,14)
>> >
>> > z <- findIndexIn(x, y)
>> > z
>> > [1] 5 3 NA
>> >
>> > 1st element of z is 5, because the 1st element of x is at the 5th
>> position in y
>> > 2nd element of z is 3, because the 2nd element of x is at the 3rd
>> position in y
>> > 3rd element of z is NA, because the 3rd element of x is not in y
>> >
>> > Of course I can write the function findIndexIn() using a for loop,
>> but
>> > in 80% of cases when I felt the urge to use "for" in R it turned out
>> > that there was already some builtin operator or function that did the
>> > trick.
>> >
>> > Suggestions, anyone?
>> > Thanks,
>> >
>> > robert
>> >
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>> >
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.

--

Bert Gunter
Genentech Nonclinical Biostatistics

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