purrr and failure in R

safely and possibly turn an error into a value you can inspect.

library(purrr)
library(dplyr)

parse_tpm <- function(text) {
  value <- suppressWarnings(as.numeric(text))
  if (is.na(value)) stop("not a number: ", text)
  value
}

safe_parse <- safely(parse_tpm)
results <- map(c("96", "fast", "104"), safe_parse)
print(map_lgl(results, ~ is.null(.x$error)))
print(compact(map(results, "result")) |> unlist())

maybe_parse <- possibly(parse_tpm, otherwise = NA_real_)
print(map_dbl(c("96", "fast"), maybe_parse))

frames <- map(1:2, ~ tibble(n = .x, squared = .x^2))
print(list_rbind(frames))

How it works

1. safely returns a list of result and error, never throwing.
2. possibly substitutes a default instead.
3. list_rbind stacks the successful results.

Keywords and builtins used here

• c
• compact
• function
• if
• library
• list_rbind
• map
• map_dbl
• map_lgl
• possibly
• print
• safely
• stop
• suppressWarnings
• tibble
• unlist

The run, in numbers

Lines

19

Characters to type

522

Tokens

151

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 86 seconds.

Type this snippet

Step 3 of 4 in purrr, step 3 of 10 in Functional & text tools.

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