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How to Concatenate Lists From Map Properties In Elixir?

4 minutes read

To concatenate lists from map properties in Elixir, you can use the Map.get/3 function to access the lists from the map, and then use the ++ operator to concatenate the lists together. This allows you to combine the elements of the lists into a single list.


What is map properties concatenation in Elixir?

Map properties concatenation in Elixir refers to the process of combining two or more maps together to create a new map that contains all the key-value pairs from the original maps. This can be done using the | operator in Elixir. When two maps are concatenated using this operator, the key-value pairs from the second map will override any duplicate keys from the first map.


For example:

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map1 = %{a: 1, b: 2}
map2 = %{b: 3, c: 4}

concatenated_map = map1 |> Map.merge(map2)
# Result: %{a: 1, b: 3, c: 4}


In this example, the Map.merge/2 function is used to concatenate map1 and map2. The resulting map concatenated_map contains the key-value pairs from both map1 and map2, with the value for key b being overridden by the value from map2.


What is the output of concatenating empty lists from map pairs in Elixir?

The output would be an empty list.


How to merge lists from map values in reverse order in Elixir?

You can achieve this by first extracting the values from the map, then merging the lists in reverse order. Here's how you can do it in Elixir:

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

values = Map.values(map)
merged_list = Enum.reverse(values) |> Enum.reduce(&(&1 ++ &2), [])

IO.inspect(merged_list)


In this code snippet:

  1. We define a map with keys and lists as values.
  2. We extract the values from the map using Map.values/1.
  3. We reverse the list of values using Enum.reverse/1.
  4. We merge the lists in reverse order using Enum.reduce/2 and the ++ operator.
  5. Finally, we print the resulting merged list.


This code will merge the lists from the map values in reverse order.


How to merge lists from map properties with different lengths in Elixir?

One way to merge lists from map properties with different lengths in Elixir is to use the Enum.zip/2 function followed by Enum.flat_map/2.


Here is an example code snippet that demonstrates how to merge lists from map properties with different lengths:

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map1 = %{a: [1, 2, 3], b: [4, 5]}
map2 = %{a: [6, 7], b: [8, 9, 10]}

merged = for {key, list1} <- map1, {_, list2} <- map2, key == _, do: Enum.zip(list1, list2)
            |> Enum.flat_map(&(&1))

IO.inspect(merged)


In this example, we first iterate over the keys and values of map1 and map2, filtering out only the keys that match. We then use Enum.zip/2 to merge the corresponding lists together and Enum.flat_map/2 to flatten the result.


After running this code, the merged variable will contain the merged lists from the map properties with different lengths.


How to combine lists from map keys with integer values in Elixir?

One way to combine lists from map keys with integer values in Elixir is to use the Enum.reduce/3 function. Here is an example code snippet that demonstrates this:

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map = %{"a" => [1, 2, 3], "b" => [4, 5, 6], "c" => [7, 8, 9]}
combined_list = Enum.reduce(map, [], fn {_, list}, acc ->
  acc ++ list
end)

IO.inspect(combined_list)


In this code snippet, we first define a map map where the keys are strings and the values are lists of integers. We then use Enum.reduce/3 to iterate over the key-value pairs in the map and accumulate the lists into a single list combined_list. Finally, we output the combined_list using IO.inspect/2.


This will result in a list containing all the integer values from the lists associated with the keys in the map.


How to concatenate lists with a specific order from map values in Elixir?

You can concatenate lists in Elixir with a specific order from map values by using the Enum.reduce/3 function. Here's an example implementation:

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map = %{"first" => [1, 2, 3], "second" => [4, 5, 6], "third" => [7, 8, 9]}
order = ["third", "first", "second"]

result = Enum.reduce(order, [], fn(key, acc) ->
  Map.get(map, key, []) ++ acc
end)

IO.inspect(result)


In this example, we have a map map with three keys ("first", "second", "third") and corresponding lists as values. We also have a list order that specifies the order in which we want to concatenate the lists.


We use Enum.reduce/3 to iterate over the keys in order, retrieving the corresponding list from the map using Map.get/3 and concatenating it with the accumulator list acc. Finally, we output the concatenated list using IO.inspect.


Running this code will output the concatenated list with the lists from the map concatenated in the order specified by the order list.

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