Question
I have a data frame with two columns. First column contains categories such as "First", "Second", "Third", and the second column has numbers that represent the number of times I saw the specific groups from "Category".
For example:
Category Frequency
First 10
First 15
First 5
Second 2
Third 14
Third 20
Second 3
I want to sort the data by Category and sum all the Frequencies:
Category Frequency
First 30
Second 5
Third 34
How would I do this in R?
Answer
Using aggregate
:
aggregate(x$Frequency, by=list(Category=x$Category), FUN=sum)
Category x
1 First 30
2 Second 5
3 Third 34
In the example above, multiple dimensions can be specified in the list
.
Multiple aggregated metrics of the same data type can be incorporated via
cbind
:
aggregate(cbind(x$Frequency, x$Metric2, x$Metric3) ...
(embedding @thelatemail comment), aggregate
has a formula interface too
aggregate(Frequency ~ Category, x, sum)
Or if you want to aggregate multiple columns, you could use the .
notation
(works for one column too)
aggregate(. ~ Category, x, sum)
or tapply
:
tapply(x$Frequency, x$Category, FUN=sum)
First Second Third
30 5 34
Using this data:
x <- data.frame(Category=factor(c("First", "First", "First", "Second",
"Third", "Third", "Second")),
Frequency=c(10,15,5,2,14,20,3))