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I want to be able to extract the Nth item of a tuple in a pipeline, without using with or otherwise breaking up the pipeline. Enum.at would work perfectly except for the fact that a tuple is not an enum.
Here's a motivating example:
colors = %{red: 1, green: 2, blue: 3}
data = [:red, :red, :blue]
data
|> Enum.map(&Map.fetch(colors, &1))
|> Enum.unzip
This returns {[:ok, :ok, :ok], [1, 1, 3]} and let's say I just want to extract [1, 1, 3]
(For this specific case I could use fetch! but for my actual code that doesn't exist.)
I could add on
|> Tuple.to_list
|> Enum.at(1)
Is there a better way of doing this that doesn't require creating a temporary list out of each tuple?
660
If you need to get the second element from a list of tuples, use a list comprehension. Copied! We used a list comprehension to get a new list that contains the second element of each tuple. List comprehensions are used to perform some operation for every element, or select a subset of elements that meet a condition.
Elixir tuples are stored contiguously in memory and are accessed by index. A tuple literal uses a pair of curly braces {} . The elem/2 function is used to access a data item in a tuple. The length of a tuple can be found with the tuple_size/1 function.
Use indexing to get the first element of each tuple Use a for-loop to iterate through a list of tuples. Within the for-loop, use the indexing tuple[0] to access the first element of each tuple, and append it.
Use Kernel.elem/2:
iex(1)> {[:ok, :ok, :ok], [1, 1, 3]} |> elem(1)
[1, 1, 3]
Pattern Match can help
{ _status, required_value } =
data
|> Enum.map(&Map.fetch(colors, &1))
|> Enum.unzip
You can ignore the _status.
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