group_by in R

Grouping persists until you ungroup, which is the usual source of bugs.

library(dplyr)

runs <- tibble(
  lang = c("r", "r", "python", "python"),
  day = c("mon", "tue", "mon", "tue"),
  tpm = c(88, 96, 104, 99)
)

grouped <- group_by(runs, lang)
print(group_vars(grouped))
print(mutate(grouped, share = round(tpm / sum(tpm), 3)))

summary <- summarise(group_by(runs, lang, day), tpm = mean(tpm),
                     .groups = "drop_last")
print(group_vars(summary))
print(ungroup(summary))

How it works

1. Every verb after group_by works within the groups.
2. summarize peels one grouping level off.
3. ungroup before returning, or the caller inherits the grouping.

Keywords and builtins used here

• c
• group_by
• group_vars
• library
• mean
• mutate
• print
• round
• sum
• summarise
• tibble
• ungroup

The run, in numbers

Lines

16

Characters to type

392

Tokens

130

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 78 seconds.

Type this snippet

Step 1 of 4 in Grouping, step 14 of 27 in dplyr.

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