我有一个这样的清单清单：

[
    ["5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42", "1538077790705827"],
     ["5b71d7e458c37fa04a7ce768","5b3f77502dfe0deeb8912b42","1538078530667847"],
     ["5b71d7e458c37fa04a7ce768","5b3f77502dfe0deeb8912b42","1538077778390908"],
     ["5b71d7e458c37fa04a7ce768","5bad45b1e990057961313822","1538082492283531"]
]

我想将其转换为类似的列表：

[ 
  {"5b3f77502dfe0deeb8912b42",
   [{"5b71d7e458c37fa04a7ce768","5b3f77502dfe0deeb8912b42", "1538077790705827"},
    {"5b71d7e458c37fa04a7ce768","5b3f77502dfe0deeb8912b42", "1538078530667847"},
    {"5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42" ,"1538077778390908"}
   ]},

{"5bad45b1e990057961313822",
   [{"5b71d7e458c37fa04a7ce768","5bad45b1e990057961313822","1538082492283531"}
   ]}
]

因此，键将在原始列表的第二项之外创建元组

[“ 5b71d7e458c37fa04a7ce768”， “ 5b3f77502dfe0deeb8912b42” ，“ 1538077790705827”]，

首先，使用Enum.group_by列表的第二个元素。 然后，将结果映射值的每个值映射到List.to_tuple 。 Enum.map与地图Enum.map使用时会自动将每个键/值对转换为元组。

list = [
  ["5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42", "1538077790705827"],
  ["5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42", "1538078530667847"],
  ["5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42", "1538077778390908"],
  ["5b71d7e458c37fa04a7ce768", "5bad45b1e990057961313822", "1538082492283531"]
]

list
|> Enum.group_by(&Enum.at(&1, 1))
|> Enum.map(fn {k, v} -> {k, Enum.map(v, &List.to_tuple/1)} end)
|> IO.inspect

输出：

[
  {"5b3f77502dfe0deeb8912b42",
   [
     {"5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42",
      "1538077790705827"},
     {"5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42",
      "1538078530667847"},
     {"5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42",
      "1538077778390908"}
   ]},
  {"5bad45b1e990057961313822",
   [
     {"5b71d7e458c37fa04a7ce768", "5bad45b1e990057961313822",
      "1538082492283531"}
   ]}
]

我将使用地图根据第二个元素对列表列表进行索引，然后使用Enum.map/2和List.to_tuple/1对其进行转换。

如果

l = [
    ["5b71d7e458c37fa04a7ce768", "5b3f77502dfe0deeb8912b42", "1538077790705827"],
     ["5b71d7e458c37fa04a7ce768","5b3f77502dfe0deeb8912b42","1538078530667847"],
     ["5b71d7e458c37fa04a7ce768","5b3f77502dfe0deeb8912b42","1538077778390908"],
     ["5b71d7e458c37fa04a7ce768","5bad45b1e990057961313822","1538082492283531"]
]

然后

l
    |> Enum.reduce(%{}, fn [a,b,c], acc -> put_in(acc[b], (acc[b] && acc[b] || []) ++ [[a,b,c]]) end)
    |> Enum.map(fn {a,b} -> {a, Enum.map(b, &List.to_tuple/1)} end)

做工作。