how to search for unique elements by the first column of a multidimensional array

Question

I am trying to find a way how to create a new array from a multidimensional array by taking only elements that are unique in the first column, for example if I have an array

Answer 1

main = [[1, 2, 3], [1, 3, 4], [2, 4, 5], [3, 6, 5]]
used = []
new = [[sub, used.append(sub[0])][0] for sub in main if sub[0] not in used]
print(new)
# Output: [[1, 2, 3], [2, 3, 4], [3, 6, 5]]