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I can get the first element of every tuple if I create the list at the same time, for example
[element(2,X) || X <- [{1,2},{3,4}]].
[2,4]
This works as it should. I want to be able to create the list before I try to do anything with it
Ex: Create the list
X = [{1,2,3},{3,4,5}].
[{1,2,3},{3,4,5}]
Then get the first element of each tuple
element(1,X).
But I get the error
** exception error: bad argument
in function element/2
called as element(1,[{1,2,3},{3,4,5}])
I want this code to give the same results that my first example gave
813
We can iterate through the entire list of tuples and get first by using the index, index-0 will give the first element in each tuple in a list.
To get the first element of each tuple in a list: Declare a new variable and set it to an empty list. Use a for loop to iterate over the list of tuples. On each iteration, append the first tuple element to the new list.
The List is a structure used to store a collection of data items. In Erlang, Lists are created by enclosing the values in square brackets.
Use List Comprehension with a generator(<-)
X = [{1,2,3},{3,4,5}].
[A || {A,_,_} <- X].
This is saying that we want to print element A, where A is taken from the tuple {A,_,_}(a tuple which we generate from each tuple in X). Because we are only selecting A and don't care about the second and third element, they are set equal to _.
Output
1> X = [{1,2,3},{3,4,5}].
[{1,2,3},{3,4,5}]
2> [A || {A,_,_} <- X].
[1,3]
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