[R] Help on aggregate method

[Stella Pachidi]

Dear R experts,

I would really appreciate if you had an idea on how to use more
efficiently the aggregate method:

More specifically, I would like to calculate the mean of certain
values on a data frame,  grouped by various attributes, and then
create a new column in the data frame that will have the corresponding
mean for every row. I attach part of my code:

matchMean <- function(ind,dataTable,aggrTable)
{
    index <- which((aggrTable[,1]==dataTable[["Attr1"]][ind]) &
(aggrTable[,2]==dataTable[["Attr2"]][ind]))
    as.numeric(aggrTable[index,3])
}

avgDur <- aggregate(ap.dat[["Dur"]], by = list(ap.dat[["Attr1"]],
ap.dat[["Attr2"]]), FUN="mean")
meanDur <- sapply((1:length(ap.dat[,1])), FUN=matchMean, ap.dat, avgDur)
ap.dat <- cbind (ap.dat, meanDur)

As I deal with very large dataset, it takes long time to run my
matching function, so if you had an idea on how to automate more this
matching process I would be really grateful.

Thank you very much in advance!

Kind regards,
Stella



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Stella Pachidi
Master in Business Informatics student
Utrecht University