[R] How to apply a function to all combinations of the values of 2 or more variables?

[Lane, Jim]

 Phil: thank you very much, that's exactly what I was looking for! Why I
couldn't have figured that out from the doc for myself is another
question:-)

-Jim

-----Original Message-----
From: Phil Spector [mailto:spector at stat.berkeley.edu] 
Sent: 2009, April, 15 1:21 PM
To: Lane, Jim
Subject: Re: [R] How to apply a function to all combinations of the
values of 2 or more variables?

by(mf,list(mf$centre,mf$complex),summary)

                                        - Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu


On Wed, 15 Apr 2009, Lane, Jim wrote:

> Hi, All
>
> Forgive me if this is a stupid newbie question. I'm having no luck 
> googling an answer to this, probably because I don't know the right R 
> terminology to frame my question. I want to know how to run an R 
> function on each combination of the values of 2 or more variables. In 
> SAS-speak this is multiple "BY variables" or "CLASS variables".
>
> In R I've figured out how to do what I want with one by value.
>
> by(mf,mf$centre,summary)
>
> Centre is one of the columns in the data frame "mf" which looks like
> this:
>
> names(mf)
> [1] "centre"   "complex"  "appl"     "pool"     "month"    "alloc_gb"
>
> I'd like to analyze, for example, by complex within centre. This has a

> manageable number of combinations:
>
> table(mf$centre,mf$complex)
>
>                   A      B      C      D      E      F      G      H
> I      J      K      L
>  B         0      0      0      0      0      0      0      0      0
> 0      0  60574      0
>  G        44    209      0  94613      0    156      0   2541      0
> 748      0      0 215511
>  O         0      0      0      0      0      0   3446      0    676
> 0  84400      0      0
>  Q         0      0    298      0  66277      0      0      0      0
> 0      0      0      0
>
> In SAS what I'm after is something like:
>
> Proc summary nway;
> class centre complex;
> var alloc_gb;
> output out=s sum=;
> run;
>
> How do I get something similar in R?
>
> Jim Lane
> Capacity Planner
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>
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>
> - H. W. Fowler, Modern English Usage
>
>
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