Add a wrapper around functions you call in map

Roel M. Hogervorst


Categories: R Tags: hacks purrr

I recently wanted to download hundreds of files However I had to wait for a long time, didn’t know how far I was (could have checked the folder)

A solution to help me, because I’m easily bored, is to get feedback on the progress. I wrapped a messaging function around the download function, that I called many times.

#' download a file and give feedback
download_file <- function(file){
    filename <- basename(file)
        print(paste("file exists: ",filename))
        print(paste0("downloading file:", file))

        curl::curl_download(url = file,destfile = paste0("data/",filename),mode = "wb")

I then apply the function to a list of web adresses:

map(paste0("first part of the link",
           formatC(1:latest_episode, width = 3,flag = 0),".txt"), download_file)

!!!! The bottleneck was here not in the repetition, but in me, I am not a patient man. I wrapped the same functionality around readr::read_lines and it was horribly slow!


read_lines2 <- function(file){

## read_lines2: user 2.00, system 1.71, elapsed 17.32
## read_lines: user 0.61, system 1.05, elapsed 1.69  (crazy slowdown by print!)