Elixir:将具有相同地图键的列表合并到一个地图

Question

如何在elixir中转换此列表

[
%{key1: 1, key2: 2, key3: 3},
%{key1: 4, key2: 5, key3: 6},
%{key1: 7, key2: 8, key3: 9}
]

到这张地图

%{key1: [1, 4, 7], key2: [2, 5, 8], key3: [3, 6, 9])

？

Answer 1

你可以两次通过; 第一个将所有内容展平为单个一维的键值对列表,然后第二个按键组合.

input = [
  %{key1: 1, key2: 2, key3: 3},
  %{key1: 4, key2: 5, key3: 6},
  %{key1: 7, key2: 8, key3: 9}
]

input
|> Enum.flat_map(fn m -> Map.to_list(m) end) 
|> Enum.group_by(fn {k, _} -> k end, fn {_, v} -> v end) 

产量

%{key1: [1, 4, 7], key2: [2, 5, 8], key3: [3, 6, 9]}

Answer 2

Enum.reduce(input, %{key1: [], key2: [], key3: []}, fn m, acc ->\n  Map.merge(acc, m, fn _k, v1, v2 -> v1 ++ [v2] end)\nend)\n#\xe2\x87\x92\xc2\xa0%{key1: [1, 4, 7], key2: [2, 5, 8], key3: [3, 6, 9]}\n

\n\n

或者，没有预先硬编码的累加器：

\n\n

Enum.reduce(input, %{}, fn m, acc ->\n  Map.merge(acc, m, fn\n    _k, v1, v2 when is_list(v1) ->\n      :lists.reverse([v2 | :lists.reverse(v1)])\n    _k, v1, v2 -> [v1, v2]\n  end)\nend)\n#\xe2\x87\x92\xc2\xa0%{key1: [1, 4, 7], key2: [2, 5, 8], key3: [3, 6, 9]}\n

\n