[R] Equivalent to a BY command in SAS

From: zerfetzen <zerfetzen_at_yahoo.com>
Date: Sun, 13 Apr 2008 19:36:38 -0700 (PDT)

I'm very new to R and absolutely love it. Does anyone know how to use something in R that functions like a BY command in SAS?

For example, let's say you have a variable x, and you want to see the mean. Easy...

> mean(x)

But what if you want to see the mean of x conditional on another discrete variable? My best attempts so far are something like...

> mean(x, y_cat=1)

...which of course doesn't work. I have downloaded plenty of R user guides that are very informative, but am not seeing much on detailed descriptives or data manipulation (for my life, I can't figure out how to sort an attached data frame, but that's another issue). Thanks.

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