How to group and count occurrences of values in Elixir's list
Join Elixir newsletter
Subscribe to receive Elixir news to your inbox every two weeks.
Expand your skills
Download free e-books, watch expert tech talks, and explore open-source projects. Everything you need to grow as a developer - completely free.
If you ever had to count occurrences of values in Elixir's list, this short post might be helpful for you!
Let's assume that the input contains a list of people names:
people = [
%{name: "John"},
%{name: "Tom"},
%{name: "John"},
%{name: "David"}
]Our goal here is to count occurrences of names so that in the end we'll get this summary:
%{"David" => 1, "John" => 2, "Tom" => 1}In Elixir, it's super easy! You can use Enum.frequencies_by/2 to achieve that in a simple one-liner:
iex > Enum.frequencies_by(people, & &1.name)
%{"David" => 1, "John" => 2, "Tom" => 1}Work with a team that keeps learning and building better software every day.
Related posts
Dive deeper into this topic with these related posts
You might also like
Discover more content from this category
By default in the test env, Phoenix doesn't show Logger.debug/Logger.info outputs in the console.
Sometimes you need to do some database operations at once. A simple example: User-A transfers money to User-B. Updating just one balance at the time creates a risk of data desynchronization. What if the first DB operation goes well but updating the second user’s data fails? Sounds like a hard to catch vulnerability.
TLDR: With jest-extended package you can write: expect([...set]).toIncludeSameMembers([value1, value2]);. If you are looking to a native, but longer solution scroll down a bit.