aggregate a column by sum and another column by mean at the same time

Question

I want to use aggregate function on a date frame but sum one column and take average of another column.

Here is an example data frame

Manager   Categ         


        

Answer 1

There are several ways to do this. Here are some that I like (all assuming we're starting with a data.frame named "mydf"):

Using ave and unique

unique(within(mydf, {
  Amount <- ave(Amount, Manager, FUN = sum)
  SqFt <- ave(SqFt, Manager, FUN = mean)
  rm(Category)
}))
#   Manager Amount SqFt
# 1     Joe    200  500
# 2   Alice    325  700

---

Using data.table:

library(data.table)
DT <- data.table(mydf)
DT[, list(Amount = sum(Amount), SqFt = mean(SqFt)), by = "Manager"]
#    Manager Amount SqFt
# 1:     Joe    200  500
# 2:   Alice    325  700

---

Using "sqldf":

library(sqldf)
sqldf("select Manager, sum(Amount) `Amount`, 
      avg(SqFt) `SqFt` from mydf group by Manager")

---

Using aggregate and merge:

merge(aggregate(Amount ~ Manager, mydf, sum), 
      aggregate(SqFt ~ Manager, mydf, mean))

Answer 2

You can use the summarise function with ddply in the plyr package:

library(plyr)
ddply(mtcars,.(cyl),summarise,TotalWt=sum(wt),AveHP=mean(hp))
  cyl TotalWt     AveHP
1   4  25.143  82.63636
2   6  21.820 122.28571
3   8  55.989 209.21429