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Purrrfecting our function

We are still perfecting our function to detect if a list of URLs contains elements that are not available.

Let's review what we have coded so far:

  • An error extractor, by combining safely() and map(.x, "error").
  • A "non-null" extractor, by combining safely() and discard(.x, is.null).
  • A 404 generator, by using possibly(.x, otherwise = 404), which was turned into a function.

We'll change the behavior of this function a bit: you now want to be able to choose between returning either the results or the errors.

This will allow you to answer two questions with just one function: which are the unreachable URLs, and which are the reachable ones? To do this, you'll add a parameter called "type" inside this function.

The urls vector and safe_read() are available in your workspace.

This exercise is part of the course

Intermediate Functional Programming with purrr

View Course

Exercise instructions

Complete the function definition.

  • Map safe_read() to the list of URLs.
  • Set the names of the result to the list of URLs.
  • Transpose the result into a list of $result and $error.
  • Use pluck() to extract the type element.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

# Complete the function definition
url_tester <- function(url_list, type = c("result", "error")) {
  type <- match.arg(type)
  url_list %>%
    # Apply safe_read to each URL
    ___(___) %>%
    # Set the names to the URLs
    ___(___) %>%
    # Transpose into a list of $result and $error
    ___()  %>%
    # Pluck the type element
    ___(___) 
}

# Try this function on the urls object
url_tester(urls, type = "error")
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