[BioC] problem about set operation and computation after split

[Steve Lianoglou]

Hi,

Your questions aren't bioconductor/bioinformatics related, and should
really go to R-help.

Still, I'll offer one suggestion -- for more help, please repost the
question to r-help:

On Thu, Jun 7, 2012 at 4:36 AM, bestbird7788 [guest]
<guest at bioconductor.org> wrote:
>
> hi,
>    I met some problems in R, please help me.
> 1. How to do a intersect operation among several groups in one list, without a loop statement? (I think It may be a list)
>   create data:
>   myData <- data.frame(product = c(1,2,3,1,2,3,1,2,2), year=c(2009,2009,2009,2010,2010,2010,2011,2011,2011),value=c(1104,608,606,1504,508,1312,900,1100,800))
>   mySplit<- split(myData,myData$year)
>   mySplit
> $`2009`
>  product year value
> 1       1 2009  1104
> 2       2 2009   608
> 3       3 2009   606
>
> $`2010`
>  product year value
> 4       1 2010  1504
> 5       2 2010   508
> 6       3 2010  1312
>
> $`2011`
>  product year value
> 7       1 2011   900
> 8       2 2011  1100
> 9       2 2011   800
>    I want to get intersection of product between every year. I know the basic is:
>    intersect(intersect(mySplit[[1]]$product, mySplit[[2]]$product),mySplit[[3]]$product)
>    this will give the correct answer:
>    [1] 1 2
>    above code lacks reusability, so It should use a for loop:
>    myIntersect<-mySplit[[1]]$product
>    for (i in 1:length(mySplit)-1){
>        myIntersect<-intersect(myIntersect,mySplit[[i+1]]$product)
>    }
>    It's correct too, but stll too complex, so my question is:
>    Can I do the same thing just use another similar intersect function (without for/repeat/while).
>    What's this simple function's name ?

I think your for loop is "fine", but if you want a more functional way
of doing it, you could do:

myi <- Reduce(intersect, lapply(mySplit, '[[', 'product'))

-steve

-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact