[R] indexing problem

[diana]

ah sorry, here's an example:
 > dm = cbind(1:2,11:12,101:102)
 > dm
      [,1] [,2] [,3]
[1,]    1   11  101
[2,]    2   12  102

 > idx=cbind(c(1,2),c(2,3))
 > idx
      [,1] [,2]
[1,]    1    2
[2,]    2    3

the result I want to get:
1   11
12 102

that is: each row of idx gives the column index in dm

diana

Sundar Dorai-Raj wrote:
> 
> 
> diana.chirac at free.fr wrote:
> 
>> Hi,
>>
>> I have the following indexing problem, can you help me please ?
>>
>> Given:
>> dm = a data.frame or a matrix dm,
>> idx = a 2 columns (or any number) matrix with the same number of rows 
>> as dm
>>
>> I want get a subset of dm, for each row, the columns which
>> specified by idx.
>>
>> thank you, diana
>>
> 
> Diana,
>   From what I gather it appears as if you want to split dm by all the 
> unique rows of idx? Is that right? If so, you can do the following:
> 
> x <- split(dm, do.call("paste", as.data.frame(idx))
> 
> This will split dm into a list with each element a subset of dm 
> corresponding to a unique row in idx. The length of the x will be the 
> number of unique rows in idx.
> 
> If this is not what you want, please provide an example and what you 
> expect to see.
> 
> --sundar
> 
> 
> 
>