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
315 Front St W
6th Floor - H14
Toronto, Ontario CANADA
M5V 3A4
416-348-6024

Display of superior knowledge is as great a vulgarity
as display of superior wealth - greater indeed, inasmuch 
as knowledge should tend more definitely than wealth
towards discretion and good manners.

- H. W. Fowler, Modern English Usage


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