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Alex Rivera
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Say I have a data.frame object: df <- data.frame(name=c('black','black','black','red','red'), type=c('chair','chair','sofa','sofa','plate'), num=c(4,5,12,4,3)) Now I want to count the number of rows (observations) of for each combination of name and type . This can be done like so: table(df[ , c("name","type")]) or possibly also with plyr , (though I am not sure how). However, how do I get the results incorporated into the original data frame? So that the results will look like this: df # name type num count # 1 black chair 4 2 # 2 black chair 5 2 # 3 black sofa 12 1 # 4 red sofa 4 1 # 5 red plate 3 1 where count now stores the results from the aggregation. A solution with plyr could be interesting to learn as well, though I would like to see how this is done with base R.
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