I have a contingency table of counts, and I want to extend it with corresponding proportions of each group.
Some sample data (tips data set from ggplot2 package):
library(ggplot2)
head(tips, 3)
# total_bill tip sex smoker day time size
# 1 17 1.0 Female No Sun Dinner 2
# 2 10 1.7 Male No Sun Dinner 3
# 3 21 3.5 Male No Sun Dinner 3
First, use table to count smoker vs non-smoker, and nrow to count total number of subjects:
table(tips$smoker)
# No Yes
# 151 93
nrow(tips)
# [1] 244
Then, I want to calculate percentage of smokers vs. non smokers. Something like this (ugly code):
# percentage of smokers
options(digits = 2)
transform(as.data.frame(table(tips$smoker)), percentage_column = Freq / nrow(tips) * 100)
# Var1 Freq percentage_column
# 1 No 151 62
# 2 Yes 93 38
Is there a better way to do this?
(even better it would be to do this on a set of columns (which I enumerate) and have output somewhat nicely formatted) (e.g., smoker, day, and time)
If it's conciseness you're after, you might like:
prop.table(table(tips$smoker))
and then scale by 100 and round if you like. Or more like your exact output:
tbl <- table(tips$smoker)
cbind(tbl,prop.table(tbl))
If you wanted to do this for multiple columns, there are lots of different directions you could go depending on what your tastes tell you is clean looking output, but here's one option:
tblFun <- function(x){
tbl <- table(x)
res <- cbind(tbl,round(prop.table(tbl)*100,2))
colnames(res) <- c('Count','Percentage')
res
}
do.call(rbind,lapply(tips[3:6],tblFun))
Count Percentage
Female 87 35.66
Male 157 64.34
No 151 61.89
Yes 93 38.11
Fri 19 7.79
Sat 87 35.66
Sun 76 31.15
Thur 62 25.41
Dinner 176 72.13
Lunch 68 27.87
If you don't like stack the different tables on top of each other, you can ditch the do.call and leave them in a list.