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katrinleinweber's solution

to Phone Number in the R Track

Published at Apr 21 2019 · 0 comments
Test suite

Clean up user-entered phone numbers so that they can be sent SMS messages.

The North American Numbering Plan (NANP) is a telephone numbering system used by many countries in North America like the United States, Canada or Bermuda. All NANP-countries share the same international country code: 1.

NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area code, commonly known as area code, followed by a seven-digit local number. The first three digits of the local number represent the exchange code, followed by the unique four-digit number which is the subscriber number.

The format is usually represented as


where N is any digit from 2 through 9 and X is any digit from 0 through 9.

Your task is to clean up differently formatted telephone numbers by removing punctuation and the country code (1) if present.

For example, the inputs

  • +1 (613)-995-0253
  • 613-995-0253
  • 1 613 995 0253
  • 613.995.0253

should all produce the output


Note: As this exercise only deals with telephone numbers used in NANP-countries, only 1 is considered a valid country code.


See this guide for instructions on how to setup your local R environment.

How to implement your solution

In each problem folder, there is a file named <exercise_name>.R containing a function that returns a NULL value. Place your implementation inside the body of the function.

How to run tests

Inside of RStudio, simply execute the test_<exercise_name>.R script. This can be conveniently done with testthat's auto_test function. Because exercism code and tests are in the same folder, use this same path for both code_path and test_path parameters. On the command-line, you can also run Rscript test_<exercise_name>.R.


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Submitting Incomplete Solutions

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context("phone number")

test_that("cleans the number", {
  expect_equal(parse_phone_number("(223) 456-7890"), "2234567890")

test_that("cleans numbers with dots", {
  expect_equal(parse_phone_number("223.456.7890"), "2234567890")

test_that("cleans numbers with multiple spaces", {
  expect_equal(parse_phone_number("223 456   7890   "), "2234567890")

test_that("invalid when 9 digits", {
  expect_equal(parse_phone_number("123456789"), NULL)

test_that("invalid when 11 digits and not starting with a 1", {
  expect_equal(parse_phone_number("22234567890"), NULL)

test_that("valid when 11 digits and starting with 1", {
  expect_equal(parse_phone_number("12234567890"), "2234567890")

test_that("invalid when more than 11 digits", {
  expect_equal(parse_phone_number("321234567890"), NULL)

test_that("invalid with letters", {
  expect_equal(parse_phone_number("123-abc-7890"), NULL)

test_that("invalid with punctuations", {
  expect_equal(parse_phone_number("123-@:!-7890"), NULL)

test_that("invalid if area code does not start with 2-9", {
  expect_equal(parse_phone_number("(123) 456-7890"), NULL)

test_that("invalid if exchange code does not start with 2-9", {
  expect_equal(parse_phone_number("(223) 056-7890"), NULL)

message("All tests passed for exercise: phone-number")

parse_phone_number <- function(number_string) {
  number_string %>%
    # remove non-digit characters
    gsub(pattern = "\\D",
         replacement = "",
         x = .) %>%
    # extract valid number pattern
         x = ., value = TRUE) %>%
    unlist() %>%
    paste(collapse = "") ->
  # handle 9 digits edge case here, to avoid "subscript out of bounds" error later
  if (phone_number == "")
    nchar(phone_number) == 10 ~ phone_number,
    # phone_number == "" ~ NULL, # not sure why this doesn't work
    TRUE ~ sub("1", "", phone_number)

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