Exercise · beginner · 8 min

Normalize emails under a declared policy

This system treats email addresses as case-insensitive. Trim and lowercase them — and do nothing else: dots and plus tags stay.

The rules

These rules decide what a correct result is. Your answer is checked on this dataset and on hidden datasets that follow the same rules.

Input
  contacts(id, email) — text. id is unique. Emails are ASCII and always present.

Rules (this fictional system's declared policy)
  email: remove ASCII whitespace (space, tab, CR, LF) at both ends, then lowercase the whole address.
  Do not remove dots, plus tags or anything else; do not merge contacts. Running the rule twice changes nothing.

Output (row order does not matter)
  clean(id text, email text)

The data

contacts · 12 rows

id	email
c2e40	·s.am@Shop.Example.net·
co4rf	··carol_99@MAIL.example.org··
cf5co	Sam+offers@example.COM
c3vyo	··carol_99@Example.com··
cgbcs	·bob@example.com·
cmnxs	··Sam+offers@Shop.Example.net··
crnsn	·s.am@example.COM·
c8m37	··sam+offers@mail.example.org··
c7og7	··s.am@MAIL.example.org··
cghwl	··carol_99@MAIL.example.org··
c80if	·Ann.Lee@Example.com··
c942l	dan+news+2026@example.com

What you practise

text
policies
idempotence

Your answer is also checked on hidden datasets generated from the same rules.

Download this dataset (CSV) with its data dictionary