Partition by column, order by another

I am simulating a SQL query with the following values:

rows = [(1, '2021/04', 'Shop 2', 341227.53), (2, '2021/05', 'Shop 2', 315447.24), (3, '2021/06', 'Shop 1', 1845662.35), (4, '2021/04', 'Shop 2', 21487.63), (5, '2021/05', 'Shop 1', 1489774.16), (6, '2021/06', 'Shop 1', 52489.35), (7, '2021/04', 'Shop 1', 154552.82), (8, '2021/05', 'Shop 2', 6548.49), (9, '2021/06', 'Shop 2', 387779.49)]

I want to build a dictionary of a ‘window’ function. It should partition on the third column (ex value: ‘shop1’) and order by the second column (ex value: ‘2021/06’).

So, it should look like this:

{
    'Shop 1': ['2021/04', '2021/05', ...],
    'Shop 2': [...],
    ...
}

Is there a way to do that such that I could define a lambda function taking two arguments, for example:

window_func = lambda partition_func, order_func: ...

The above partition_func would be item[2] and the order_func would be item[3].

>Solution :

Try:

from itertools import groupby
from operator import itemgetter

rows = [
    (1, "2021/04", "Shop 2", 341227.53),
    (2, "2021/05", "Shop 2", 315447.24),
    (3, "2021/06", "Shop 1", 1845662.35),
    (4, "2021/04", "Shop 2", 21487.63),
    (5, "2021/05", "Shop 1", 1489774.16),
    (6, "2021/06", "Shop 1", 52489.35),
    (7, "2021/04", "Shop 1", 154552.82),
    (8, "2021/05", "Shop 2", 6548.49),
    (9, "2021/06", "Shop 2", 387779.49),
]

window_func = lambda partition_func, order_func: lambda x: {
    k: [order_func(v) for v in g]
    for k, g in groupby(
        sorted(x, key=lambda v: (partition_func(v), order_func(v))), partition_func
    )
}

fn = window_func(itemgetter(2), itemgetter(1))
print(fn(rows))

Prints:

{
    "Shop 1": ["2021/04", "2021/05", "2021/06", "2021/06"],
    "Shop 2": ["2021/04", "2021/04", "2021/05", "2021/05", "2021/06"],
}

EDIT: To get list of rows in the output:

window_func = lambda partition_func, order_func: lambda x: {
    k: list(g)
    for k, g in groupby(
        sorted(x, key=lambda v: (partition_func(v), order_func(v))), partition_func
    )
}

fn = window_func(itemgetter(2), itemgetter(1))
print(fn(rows))

Prints:

{
    "Shop 1": [
        (7, "2021/04", "Shop 1", 154552.82),
        (5, "2021/05", "Shop 1", 1489774.16),
        (3, "2021/06", "Shop 1", 1845662.35),
        (6, "2021/06", "Shop 1", 52489.35),
    ],
    "Shop 2": [
        (1, "2021/04", "Shop 2", 341227.53),
        (4, "2021/04", "Shop 2", 21487.63),
        (2, "2021/05", "Shop 2", 315447.24),
        (8, "2021/05", "Shop 2", 6548.49),
        (9, "2021/06", "Shop 2", 387779.49),
    ],
}