# Re: [R] extracting row means from a list

From: Liaw, Andy <andy_liaw_at_merck.com>
Date: Wed 20 Jul 2005 - 08:24:56 EST

Justone more comment in addition to Sundar's solution:

If these are all numeric matrices, I would read them into R as such, instead of data frames. Actually, I would read them all into a 3-dimensional array (2000 x 6 x # of files). Assuming you have such an array, then you can do something like:

> ## get your example into an array: need the abind package.
> bar <- do.call("abind", c(lapply(foo, as.matrix), along=3))
> str(bar)

num [1:100, 1:6, 1:10] -0.78981 0.31939 -0.00819 1.59346 1.20498 ...

• attr(*, "dimnames")=List of 3 ..\$ : chr [1:100] "1" "2" "3" "4" ... ..\$ : chr [1:6] "x1" "x2" "x3" "x4" ... ..\$ : NULL
> str(m <- rowMeans(bar, dims=2))
num [1:100, 1:6] -0.4401 0.5463 -0.0572 -0.1314 0.5177 ...
• attr(*, "dimnames")=List of 2 ..\$ : chr [1:100] "1" "2" "3" "4" ... ..\$ : chr [1:6] "x1" "x2" "x3" "x4" ...

Andy

> -----Original Message-----
> From: r-help-bounces@stat.math.ethz.ch
> [mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Andy Bunn
> Sent: Tuesday, July 19, 2005 3:59 PM
> To: Sundar Dorai-Raj
> Cc: R-Help
> Subject: Re: [R] extracting row means from a list
>
>
> I think about half of my question in R can be solved with a judicious
> do.call.
>
> Thanks, Andy
>
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