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