Using R aggregate function over a dataframe with names

Question

I have a dataframe in the form of:

df:

RepName, Discount
Bob,Smith , 5383.24
Johh,Doe ,  30349.21
...

The names are repeated. In the df, RepName is a factor and Discount is numeric. I want to calculate the mean per RepName. I can't seem to get the aggregate statement right.

I've tried:

#This doesn't work
repAggDiscount <- aggregate(repdf,  by = repdf$RepName, FUN = mean)

#Not what I want:
repAggDiscount <- aggregate(repdf,  by = list(repdf$RepName), FUN = mean)

I've also tried the following:

repnames <- lapply(repdf$RepName, toString)
repAggDiscount <- aggregate(repdf,  by = repnames, FUN = mean)

But that gives me a length mismatch...

I've read the help but an example of how this should work for my data would go a long way... thanks!

For big data sets use data.table package. i.e., library(data.table); setDT(repdf)[, list(Discount = mean(Discount)), by = RepName] — David Arenburg
– David Arenburg, Commented Jun 12, 2014 at 18:46
Because the syntax isn't quite right. You're aggregating the whole data frame and not just the relevant columns the way you've written things. — A5C1D2H2I1M1N2O1R2T1
– A5C1D2H2I1M1N2O1R2T1, Commented Jun 12, 2014 at 18:47

MrFlick · Accepted Answer · 2014-06-14 04:30:17Z

1

I'm posting @AnandaMahto's answer here to close out the question. You can use the formula syntax

aggregate(Discount ~ RepName, repdf, mean)

Or you can use the by= syntax

repAggDiscount <- aggregate(repdf$Discount, by = list(repdf$RepName), FUN = mean)

The problem with your syntax was that you were trying to aggregate the whole data.frame which included the RepName column where taking the mean doesn't make sense

You could also to

repAggDiscount <- aggregate(repdf[,-1], by = repdf[,1,drop=F], FUN = mean)

which is closer to the matrix style syntax.

answered Jun 14, 2014 at 4:30

MrFlick

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