Consolidate duplicate rows

Question

I have a data frame where one column is species\' names, and the second column is abundance values. Due to the sampling procedure, some species appear more than once (i.e.,

Answer 1

This works:

library(plyr)
ddply(df,"x",numcolwise(sum))

in words: (1) split the data frame df by the "x" column; (2) for each chunk, take the sum of each numeric-valued column; (3) stick the results back into a single data frame. (dd in ddply stands for "take a d ata frame as input, return a d ata frame")

Another, possibly clearer, approach:

aggregate(y~x,data=df,FUN=sum)

See quick/elegant way to construct mean/variance summary table for a related (slightly more complex) question.