[lang-ref] ( dict_to_matrix ) ( python )

def test_dict_to_matrix():
    # defaultdict(lambda: defaultdict)
    from collections import defaultdict

    d = defaultdict(lambda: defaultdict(int)) # 2-d matrix

    rows = [
        ('A', 'x', 1),
        ('A', 'x', 2),
        ('A', 'y', 3),
        ('B', 'x', 10),
    ]

    for k1, k2, v in rows:
        d[k1][k2] += v

    assert d['A']['x'] == 3
    assert d['A']['y'] == 3
    assert d['B']['x'] == 10