problem about set operation and computation after split in R language

[bird best]

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 ?

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?

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

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

[bird best]

can anyone help me?

[Campbell Ritchie]

Welcome to the Ranch

Maybe nobody can help, sorry. Maybe nobody around here knows R. If you find another forum, feel free to post, but be sure to tell them you posted here, too.