Aggregate R sum

Question

I\'m writting my first program in R and as a newbie I\'m having some troubles, hope you can help me.

I\'ve got a data frame like this:

> v1<-c         


        

Answer 1

This is fairly straightforward with the plyr library.

library("plyr")
ddply(datos, .(Position), colwise(sum))

If you have additional non-numeric columns that shouldn't be averaged, you can use

ddply(datos, .(Position), numcolwise(sum))

Answer 2

ag_df <-- aggregate(.~Position,data=datos,sum)

should give you a data frame containing the sums of the "a" values for each of the positions. The trick here is the . in the formula represents a list of all the "non-grouping" variables in the formula.

Note that you can get much the same result with:

sumdf <- rowsum(datos,datos$Position,na.rm=T)

Except that includes the sums of the positions as well!

If you DON'T want all non-group columns aggregated, you can use cbind as in:

sumdf1 <- aggregate(cbind(a1,a3)~datos$Position,datos,sum)

That sums only the a1 and a3 columns.

Answer 3

You need to tell the aggregate function to use sum, as the default is for it to get the mean of each category. For example:

aggregate(datos[,c("a1","a2","a3")], by=list(datos$Position), "sum")