[R] aggregation-type question

[carslaw]

I seem to have a Friday afternoon block and can't see the easiest way of
doing this.

Given a data frame like:

dat <- data.frame(x = runif(100), y = runif(100), group = rep(letters[1:10],
each = 10))
> head(dat)
            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.

Thanks

David



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