RE: [R] summary statistics for lists of matrices or dataframes

From: Huntsinger, Reid <reid_huntsinger_at_merck.com>
Date: Wed 11 May 2005 - 00:42:06 EST


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@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of David Kane Sent: Tuesday, May 10, 2005 10:04 AM
To: r-help@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                

>


R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed May 11 01:43:00 2005

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:31:40 EST