Filter invalid login
While developing a website, you detect that some of the members have troubles logging in. Searching through the code you find that all logins ending with a “_” make problems. So you want to write a function that takes an array of pairs of login-names and e-mails, and outputs an array of all login-name, e-mails-pairs from the login-names that end with “_”.
If you have the input-array:
[ [ "foo", "email@example.com" ], [ "bar_", "firstname.lastname@example.org" ] ]
it should output
[ [ "bar_", "email@example.com" ] ]