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

[Mike Lawrence]

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On Wed, Apr 15, 2009 at 2:03 PM, Lane, Jim <jim.lane at rbc.com> 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
> RBC Financial Group
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>
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>
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>
>
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-- 
Mike Lawrence
Graduate Student
Department of Psychology
Dalhousie University

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