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:
[EMAIL PROTECTED] wrote:
Diana,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
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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