[R] Is there a "by()" function in R like in S?

Sven Garbade garbade at mip.paed.uni-muenchen.de
Mon Jan 31 12:51:18 CET 2000

Hallo R-users,

I'm a R (release 0.65) novice, but have read some about S. Is there a
similar function in R like the S function "by()" ?
This function groups data typically from a matrix by a variable and
applies a function on the grouped data. Example in S:

  > by(data, year, summary)

where "data" is a matrix containing the variable "year". After grouping
the matrix to variable "year", the function "summary" is applied to each


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