如何从列表列表中获取列表

Question

How get a list from array of arrays?

I have a List of Lists, like: [[1,2,3],[1,2,3],[1,2,3]] .

I want to have a List that contains all first elements from my List.

For example in my example, I want to have a list = [1,1,1] .

Answer 1

If you also might want to get the second/third elements of each List, you can also use transpose :

def input = [[1,2,3],[1,2,3],[1,2,3]]
def output = input.transpose()

// All the lists are joined by element index
assert output == [[1, 1, 1], [2, 2, 2], [3, 3, 3]]

// Grab the first one (1,1,1)
assert output[ 0 ] == [ 1,1,1 ]

Answer 2

If you know you always have an list of lists (ie the inner list always exists), you could do it like this:

def lists = [[1,2,3],[1,2,3],[1,2,3]]
def result = lists.collect { it[0] }
assert result == [1,1,1]