[R] summary statistics for lists of matrices or dataframes
Huntsinger, Reid
reid_huntsinger at merck.com
Tue May 10 16:42:06 CEST 2005
In such a situation you could make the list into a 3-way array. For example,
> d <- dim(z[[1]]) # all the same
> n <- length(z)
> z <- unlist(z)
> dim(z) <- c(d,n)
then you can get summary statistics for the (1,1) entries of the original
z[[1]], z[[2]] etc however you would get summary statistics for the vector
z[1,1,]. Moreover, you can vectorize this to get, say,
> rowMeans(z, dims=2)
[,1] [,2]
[1,] 3 3
[2,] 3 3
and for arbitrary functions of the entries you can use apply():
> apply(z, c(1,2), "median")
Reid Huntsinger
-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of David Kane
Sent: Tuesday, May 10, 2005 10:04 AM
To: r-help at stat.math.ethz.ch
Subject: [R] summary statistics for lists of matrices or dataframes
Is there a simple way to calculate summary statistics for all the
matrices or dataframes in a list? For example:
> z <- list(matrix(c(2,2,2,2), ncol = 2), matrix(c(4,4,4,4), ncol = 2))
> z
[[1]]
[,1] [,2]
[1,] 2 2
[2,] 2 2
[[2]]
[,1] [,2]
[1,] 4 4
[2,] 4 4
>
I would like to calculate, for example, the mean value for each
cell. I can do that the hard way as:
> (z[[1]] + z[[2]]) / 2
[,1] [,2]
[1,] 3 3
[2,] 3 3
>
But there must be an easier way. I am also interested in other
statistics (like median and sd). Since all my matrices have the same
attributes (especially row and column names), I would like to preserve
those in the answer.
Thanks,
Dave Kane
In case it matters:
> R.version
_
platform i686-pc-linux-gnu
arch i686
os linux-gnu
system i686, linux-gnu
status
major 2
minor 1.0
year 2005
month 04
day 18
language R
>
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