purrr basics in R

map returns a list; the typed variants return a vector of that type.

library(purrr)

nums <- list(1:3, 4:6, 7:9)

sums <- map_dbl(nums, sum)
firsts <- map_int(nums, ~ .x[[1]])
labels <- map_chr(nums, ~ paste(.x, collapse = "-"))
nested <- map(nums, ~ .x * 2)

pairs <- map2_dbl(1:3, 4:6, ~ .x * .y)
filtered <- keep(nums, ~ sum(.x) > 10)
total <- reduce(nums, ~ c(.x, .y))

print(sums)
print(firsts)
print(labels)
print(length(filtered))
print(pairs)
print(total)

How it works

1. map_dbl and map_int fail loudly if the result is the wrong type.
2. ~ .x is the shorthand lambda, with .x as the element.
3. keep and reduce cover filtering and folding.

Keywords and builtins used here

• c
• keep
• length
• library
• list
• map
• map2_dbl
• map_chr
• map_dbl
• map_int
• paste
• print
• reduce
• sum

The run, in numbers

Lines

19

Characters to type

394

Tokens

140

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 80 seconds.

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