[R] filling a vector with a tapply function applied to another vector

albechan alberto.casetta at satt.biz
Fri Nov 12 09:41:42 CET 2010

I have a data frame with three columns. The first one is filled with factors,
the second one with numeric values and the third one is an empty vector.
I need fill the third column with the results of the function
tapply(secondcolumn,firstcolumn,mean) so that I have for each row of the
third column the mean of the second column conditional to the factor element
in the first column.
Thank you very much for your help.
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