# [R] extracting row means from a list

Liaw, Andy andy_liaw at merck.com
Wed Jul 20 00:24:56 CEST 2005

```Justone more comment in addition to Sundar's solution:

If these are all numeric matrices, I would read them into R
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 at stat.math.ethz.ch
> [mailto:r-help-bounces at 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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