[R] aggregation-type question
david.carslaw at kcl.ac.uk
Fri Feb 8 17:33:45 CET 2013
I seem to have a Friday afternoon block and can't see the easiest way of
Given a data frame like:
dat <- data.frame(x = runif(100), y = runif(100), group = rep(letters[1:10],
each = 10))
x y group
1 0.876751503 0.6518345 a
2 0.627067150 0.8801790 a
3 0.632465192 0.1768305 a
4 0.060359554 0.8835652 a
5 0.675868776 0.7721177 a
6 0.008465241 0.5046486 a
I want to work out cor(x, y) by group, so in this case ending up with 10
correlation coefficients by group.
I'm not seeing a straightforward solution and I'd appreciate your help.
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