Row-wise work in R

rowwise turns each row into its own group, for calculations across columns.

library(dplyr)

scores <- tibble(
  lang = c("r", "python"),
  week1 = c(88, 104),
  week2 = c(96, 99),
  week3 = c(92, 101)
)

print(mutate(rowwise(scores),
             best = max(c_across(starts_with("week"))),
             mean = round(mean(c_across(week1:week3)), 1)))

print(mutate(scores, total = rowSums(across(starts_with("week")))))
print(ungroup(rowwise(scores)) |> nrow())

How it works

1. rowwise is the escape hatch when vectorization will not do.
2. c_across gathers several columns for one row.
3. pmap from purrr is often faster for the same job.

Keywords and builtins used here

• across
• c
• c_across
• library
• max
• mean
• mutate
• nrow
• print
• round
• rowSums
• rowwise
• starts_with
• tibble
• ungroup

The run, in numbers

Lines

15

Characters to type

350

Tokens

122

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 70 seconds.

Type this snippet

Step 2 of 3 in Windows & rows, step 19 of 27 in dplyr.

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