[R] select subset based on another variable

[David Winsemius]

On May 13, 2010, at 9:55 AM, David Winsemius wrote:

>
> On May 13, 2010, at 9:48 AM, Carrie Li wrote:
>
>> Hi, dear R-helpers,
>>
>> I have a simple question regarding selecting subset of a variable  
>> based on
>> another variable.
>> Here is the example:
>>
>> xx=rnorm(10)
>> id=sample(1:10, 10)
>>
>> temp=c(6, 1, 8, 2)
>>
>> Now, all I want is xx's that their id are 6, 1, 8, 2, instead of the
>> position.
>>
>> Any suggestions ?
>
> xx[temp]

I may have jumped the gun, but on reflection I am not sure that your  
question was at all clear. Is the first item desired the 6th item of  
xx or the xx item referenced by the 6th item of id? You gave a  
specification that would not allow any of us to check, since you did  
not specify a random seed. We have no way of seeing what either of  
your xx or id vectors look like since you did not provide either them  
or the desired output. If it were the second specification then  
consider this:

 > set.seed(123)
 > xx=rnorm(10)
 > id=sample(1:10, 10)
 >
 > temp=c(6, 1, 8, 2)
 > xx;id
  [1] -0.56047565 -0.23017749  1.55870831  0.07050839  0.12928774   
1.71506499
  [7]  0.46091621 -1.26506123 -0.68685285 -0.44566197
  [1]  9  7  6 10  4  8  3  2  1  5
 > xx[id[temp]]
[1] -1.2650612 -0.6868529 -0.2301775  0.4609162

>
> -- 
> David.
>>
>> Thank you all your help !!
>>
>> Carrie
>>
>> 	[[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> 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.
>
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> 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.

David Winsemius, MD
West Hartford, CT