On Wed, Jun 6, 2012 at 2:43 AM, bestbird <bestbird7...@gmail.com> wrote:
> hi,
> I met some problems in R, plz 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 ?
Take a look at Reduce()
>
> 2.how to do a relative computation after split (notice: not befor split)?
> create data:
> myData1 <- data.frame(product = c(1,2,3,1,2,3),
> year=c(2009,2009,2009,2010,2010,2010),value=c(1104,608,606,1504,508,1312),relative=0)
> mySplit1<- split(myData1,myData1$year)
> mySplit1
> $`2009`
> product year value relative
> 1 1 2009 1104 0
> 2 2 2009 608 0
> 3 3 2009 606 0
>
> $`2010`
> product year value relative
> 4 1 2010 1504 0
> 5 2 2010 508 0
> 6 3 2010 1312 0
> I want compute relative value in the every group, what I mean is , I want
> get the result is just like below:
> $`2009`
> product year value relative
> 1 1 2009 1104 0
> 2 2 2009 608 -496
> 3 3 2009 606 -2
>
> $`2010`
> product year value relative
> 4 1 2010 1504 0
> 5 2 2010 508 -996
> 6 3 2010 1312 804
> I think to use a loop maybe work, but Is there no direct method on list?
lapply ?
possibly in conjunction with sweep.
>
> 3.how to do a sorting after split, It's just like above question, what I
> want is sorting by value:
> $`2009`
> product year value relative
> 3 3 2009 606 0
> 2 2 2009 608 0
> 1 1 2009 1104 0
> $`2010`
> product year value relative
> 5 2 2010 508 0
> 6 3 2010 1312 0
> 4 1 2010 1504 0
lapply
probably you'll need order for this one.
>
> 4. how to do a filtering after split, Yes, It's just like above quetion,
> what I want is filtering out data which value is more than 1000:
> $`2009`
> product year value relative
> 1 1 2009 1104 0
> $`2010`
> product year value relative
> 4 1 2010 1504 0
> 6 3 2010 1312 0
lapply
which()
and logical indexing.
Michael
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/problem-about-set-operation-and-computation-after-split-tp4632496.html
> Sent from the R help mailing list archive at Nabble.com.
>
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