Add slowly() adverb

[jennybc]

I recently used safely() to wrap gmailr::send_message(), which I then used with pmap() to iterate over rows = recipients. I ran into sporadic rate limit problems.

It would be nice to also have a slowly() adverb for adding a little bit of delay to each call.

[DavisVaughan]

I like this idea!

library(purrr)

slowly <- function(.f, delay = 1, otherwise, quiet = TRUE) {
  .f <- as_mapper(.f)
  function(...) {
    ret <- purrr:::capture_error(.f(...), otherwise, quiet)
    Sys.sleep(delay)
    ret
  }
}

slow_log <- slowly(log)

timeit <- proc.time()

list(2, 10, 100) %>%
  map(slow_log)
#> [[1]]
#> [[1]]$result
#> [1] 0.6931472
#> 
#> [[1]]$error
#> NULL
#> 
#> 
#> [[2]]
#> [[2]]$result
#> [1] 2.302585
#> 
#> [[2]]$error
#> NULL
#> 
#> 
#> [[3]]
#> [[3]]$result
#> [1] 4.60517
#> 
#> [[3]]$error
#> NULL

proc.time() - timeit
#>    user  system elapsed 
#>   0.005   0.000   3.012

[AshesITR]

Related: https://github.com/tarakc02/ratelimitr
Maybe it's better to specify the maximum rate in such a fashion?

Reprex using ratelimitr:

library(purrr)
library(ratelimitr)

slow_log <- limit_rate(log, rate(1, 1))  # 1 run / 1 second

system.time({
  c(2, 10, 100) %>% map(slow_log)
})
#>        User      System verstrichen 
#>        0.02        0.00        2.09

As you can see, no unnecessary waiting after the last call has been made :)

[lionel-]

Should be made consistent with #333