Flattening a list: flatten

The flatten command replaces any sublists of a list by their elements.

flatten takes one argument:
L, a list.
flatten(L) returns a list which is the result of recursively replacing any elements that are lists by the elements, resulting in a list with no lists as elements.

Example.
Input:

flatten([[1,[2,3],4],[5,6]])

Output:

⎡
⎣

1,2,3,4,5,6

⎤
⎦

If the original list is a matrix, you can also use the mat2list command for this (see Section 6.40.33).