Grouped summaries in base R in R

Summarizing by group without any packages.

by_cyl <- aggregate(mpg ~ cyl, data = mtcars, FUN = mean)
two_way <- aggregate(mpg ~ cyl + am, data = mtcars, FUN = median)

counts <- table(mtcars$cyl)
cross <- table(mtcars$cyl, mtcars$am)

split_groups <- split(mtcars$mpg, mtcars$cyl)
group_sds <- sapply(split_groups, sd)
overall <- tapply(mtcars$mpg, mtcars$cyl, mean)

How it works

1. aggregate applies a function per formula group.
2. table counts categories, one-way or crossed.
3. split plus sapply, or tapply, do the same job.

Keywords and builtins used here

• aggregate
• sapply
• split
• table
• tapply

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Step 3 of 4 in Reshaping & combining, step 6 of 8 in Data frames in base R.

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