Aggregation and percentage calculation by groups

Question

I have a dataset in R of student weekly allowances by class, which looks like:

Year    ID  Class       Allowance
2013    123 Freshman    100
2013    234 Freshman    110
2013    345 Sophomore   150
2013    456 Sophomore   200
2013    567 Junior      250
2014    678 Junior      100
2014    789 Junior      230
2014    890 Freshman    110
2014    891 Freshman    250
2014    892 Sophomore   220

How can I summarize the results by group (Year/Class) to get sum and % (by group)? Getting sum seems easy with ddply by just couldn't get the % by group part right.

It works for sum:

summary <- ddply(my_data, .(Year, Class), summarize, Sum_Allow=sum(Allowance))

But it doesn't work for the percentage by group part:

summary <- ddply(my_data, .(Year, Class), summarize, Sum_Allow=sum(Allowance),
                 Allow_Pct=Allowance/sum(Allowance))

Ideal result should look like:

 Year     Class Sum_Allow Allow_Pct
 2013  Freshman       210       26%
 2013    Junior       250       31%
 2013 Sophomore       350       43%
 2014  Freshman       360       40%
 2014    Junior       330       36%
 2014 Sophomore       220       24%

I tried ddply from the plyr package, but please let me know of any way that this may work.

Answer 1

Here's a possible solution using data.table package (assuming your data called df)

library(data.table)
setDT(df)[, list(Sum_Allow = sum(Allowance)), keyby = list(Year, Class)][, 
            Allow_Pct := paste0(round(Sum_Allow/sum(Sum_Allow), 2)*100, "%"), by = Year][]

#    Year     Class Sum_Allow Allow_Pct
# 1: 2013  Freshman       210       26%
# 2: 2013    Junior       250       31%
# 3: 2013 Sophomore       350       43%
# 4: 2014  Freshman       360       40%
# 5: 2014    Junior       330       36%
# 6: 2014 Sophomore       220       24%

---

Contributed to @rawr, here's a possible base R solution

df2 <- aggregate(Allowance ~  Class + Year, df, sum)
transform(df2, Allow_pct = ave(Allowance, Year, FUN = function(x) paste0(round(x/sum(x), 2)*100, "%")))
#       Class Year Allowance Allow_pct
# 1  Freshman 2013       210       26%
# 2    Junior 2013       250       31%
# 3 Sophomore 2013       350       43%
# 4  Freshman 2014       360       40%
# 5    Junior 2014       330       36%
# 6 Sophomore 2014       220       24%

Answer 2

You could do this in two steps

my_data <- read.table(header = TRUE,
                      text = "Year    ID  Class       Allowance
2013    123 Freshman    100
2013    234 Freshman    110
2013    345 Sophomore   150
2013    456 Sophomore   200
2013    567 Junior      250
2014    678 Junior      100
2014    789 Junior      230
2014    890 Freshman    110
2014    891 Freshman    250
2014    892 Sophomore   220")

library(plyr)
(summ <- ddply(my_data, .(Year, Class), summarize, Sum_Allow=sum(Allowance)))

#   Year     Class Sum_Allow
# 1 2013  Freshman       210
# 2 2013    Junior       250
# 3 2013 Sophomore       350
# 4 2014  Freshman       360
# 5 2014    Junior       330
# 6 2014 Sophomore       220

ddply(summ, .(Year), mutate, Allow_pct = Sum_Allow / sum(Sum_Allow) * 100)

#   Year     Class Sum_Allow Allow_pct
# 1 2013  Freshman       210  25.92593
# 2 2013    Junior       250  30.86420
# 3 2013 Sophomore       350  43.20988
# 4 2014  Freshman       360  39.56044
# 5 2014    Junior       330  36.26374
# 6 2014 Sophomore       220  24.17582

I don't know if it happens for the rest of you, but when I run the original attempt, R crashes rather than throwing a warning. Or if I misspell Allow instead of allow, it crashes. I really hate that; hadley pls fix

base r forever