Alexander Clarke Alexander Clarke - 19 days ago 5
Python Question

How to find a max value in a list of lists by the last row and column

I have a list of lists and need to find the max value in the last list and last value of each list

score_matrix = [[6, 1, 2], [1, 2, 3], [3, 4, 5]]

max_value, max_index = max((x, (i, j))
for i, row in enumerate(score_matrix)
for j, x in enumerate(row))


The code should find 5 as the max value however currently finds 6.

Answer

If you only want the last value in each row to count, only include that in the generator expression:

max_value, max_index = max((row[-1], (i, len(row) - 1))
                           for i, row in enumerate(score_matrix))

row[-1] takes the last value of a given row, and len(row) - 1 produces the index of that last element.

If you also need the last row, then add those elements in a separate sequence; you can use itertools.chain() to combine two generators:

from itertools import chain
max_value, max_index = max(chain(
    ((row[-1], (i, len(row) - 1)) for i, row in enumerate(score_matrix)),
    ((c, (len(score_matrix) - 1, j)) for j, c in enumerate(score_matrix[-1]))
))

This does include that column in the last row twice, but for one extra value it's not worth slicing the last row for.

Demo:

>>> from itertools import chain
>>> score_matrix = [[6, 1, 2], [1, 2, 3], [3, 4, 5]]
>>> max(chain(
...         ((row[-1], (i, len(row) - 1)) for i, row in enumerate(score_matrix)),
...         ((c, (len(score_matrix) - 1, j)) for j, c in enumerate(score_matrix[-1]))
...     ))
(5, (2, 2))
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