[R] indexing problem

[Tony Plate]

Maybe this does what you want:

 > dm <- cbind(1:2,11:12,101:102)
 > idx <- cbind(c(1,2),c(2,3))
 > row(idx)
      [,1] [,2]
[1,]    1    1
[2,]    2    2
 > cbind(as.vector(row(idx)), as.vector(idx))
      [,1] [,2]
[1,]    1    1
[2,]    2    2
[3,]    1    2
[4,]    2    3
 > dm[cbind(as.vector(row(idx)), as.vector(idx))]
[1]   1  12  11 102
 > array(dm[cbind(as.vector(row(idx)), as.vector(idx))], dim=dim(idx))
      [,1] [,2]
[1,]    1   11
[2,]   12  102
 >

At Tuesday 12:43 PM 10/19/2004, you wrote:
>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
>>
>
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