Elixir:更新地图列表中的特定值 [英] Elixir: Update a specific value in a list of maps

问题描述

给出以下地图列表:

ball_prop_list = 
[
  %{"id" => "cue", "is_idle" => true, "velocity_x" => 0.0, "velocity_z" => 0.0, "x" => -15.0, "z" => 0.0},
  %{"id" => "ball_1", "is_idle" => true, "velocity_x" => 0.0, "velocity_z" => 0.0, "x" => 15.0, "z" => 0.0},
  %{"id" => "ball_2", "is_idle" => true, "velocity_x" => 0.0, "velocity_z" => 0.0, "x" => 17.0, "z" => 1.1},
  %{"id" => "ball_3", "is_idle" => true, "velocity_x" => 0.0, "velocity_z" => 0.0, "x" => 17.0, "z" => -1.1}
]

我该如何更改例如"id"的 velocity_x 和 velocity_y ?=>提示" ，并保持其他所有内容不变?

How do I go about changing, say, just the velocity_x and velocity_y of "id" => "cue", and keeping everything else the same?

我只是尝试创建一个具有更新值的新列表(这不一定是我的目标)，如下所示:

I've only gotten as far as trying to create a new list (which was not necessarily my goal) with updated values, such as the following:

new_prop_list = Enum.map(balls_json_list, fn(val) -> 
  if val["id"] == "cue" do
    Map.put(val, "velocity_x" velocity_vector[:x])
    Map.put(val, "velocity_z" velocity_vector[:z])
  end
end)

但这并没有解决，可能是因为我的地图没有使用原子键-到目前为止，我看到的所有其他示例都使用原子键，或者添加了新的键和值，等等.

But this didn't work out, probably because my maps do not use atom keys - every other example I've seen so far uses atom keys, or adds a new key and value, etc.

还有什么我可以尝试的吗?

Is there anything else I can try?

推荐答案

Map.put/3 不会就地修改地图(因为无法修改Elixir中的数据结构)，但是创建一个新地图.

Map.put/3 does not modify the map in-place (because no data structure in Elixir can be modified), but creates a new map.

还，您错过了两个逗号.

Also, you missed 2 commas.

new_ball_prop_list = Enum.map(ball_prop_list, fn
  %{"id" => "cue"} = map ->
    map
    |> Map.put("velocity_x", velocity[:x])
    |> Map.put("velocity_y", velocity[:y])
  other_map ->
    other_map
end)

您还可以尝试 Map.merge/2 或％{map |k1 =>v1，k2 =>v2}

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