Nest maps into each other from a list of maps

[Sebb]

Here is a solution to the same problem, but the flat list uses a ref to the parent, you are using a list of children.

Build a tree from a flat structure recursively

Enum.group_by is a little more efficient than repeatedly scanning the whole list with Enum.filter, and (IMO) is easier to understand: defmodule GroupThings do def run(data) do groups = Enum.group_by(data, & &1.parent_id) Enum.map(groups[nil], &associate_children(&1, groups)) end defp associate_children(node, groups) do children = Enum.map(groups[node.id] || [], &associate_children(&1, groups)) Map.put(node, :children, children) end end The key here is transform…