How to retrieve max key and corresponding value from the tuple in the dictionary based on the first argument of the tuple

Question

For example, if the given dictionary is as following:

dic = {('K1', 'S1'): 4.999997655759467, 
       ('k1', 'K2'): 6.1999036349232375, 
       ('K1', 'K4'): 7.999999999999876, 
       ('K2', 'K1'): 6.199940422452897, 
       ('K2', 'K3'): 7.999999999999876, 
       ('K2', 'K5'): 6.199962763954776, 
       ('K3', 'K2'): 6.199997321675397, 
       ('K3', 'K6'): 7.999998023783301, 
       ('K3', 'S2'): 9.999999999999911, 
       ('K4', 'S1'): 9.999999999999911, 
       ('K4', 'K1'): 6.199999975663285, 
       ('K4', 'K5'): 6.19999999303405, 
       ('K5', 'K2'): 6.199989058277423, 
       ('K5', 'K4'): 7.999999999999876, 
       ('K5', 'K6'): 7.999950953156936, 
       ('K6', 'S2'): 9.999999999999911, 
       ('K6', 'K3'): 7.999641214892367, 
       ('K6', 'K5'): 6.19980050493078}

And the required output is as follows:

{('K1', 'K4'): 7.999999999999876,
 ('K2', 'K3'): 7.999999999999876,
 ('K3', 'S2'): 9.999999999999911,
 ('K4', 'S1'): 9.999999999999911,
 ('K5', 'K4'): 7.999999999999876,
 ('K6', 'S2'): 9.999999999999911}

I implemented the following function, but unfortunately it can only get the value and it doesn't get the corresponding key.

def getMaxForX(number):
    return max([v for k, v in dic.items() if k[0] == number])

I don't fully understand the concept of max key and values for a dictionary?

Please suggest how I can fix this.

score 0 · Answer 1 · answered Nov 12 '19 at 13:05

0

I guess you are only appending value (v) not key (k). So update your logic of return to

return max([k, v for k, v in Q_values.items() if k[0] == number])

answered Nov 12 '19 at 13:05

Yash Khatri

27
1
2

This gives an error as well as with the this: return max([[k, v] for k, v in dic.items() if k[0] == number]) it shows ValueError: max() arg is an empty sequence – Leekhamxay Nov 12 '19 at 13:37

ekhumoro · Accepted Answer · 2019-11-13T17:24:38.507

So you want to group by the first element of the key (K1, K2, K3, ...), and then find the maximum of each group based on the value:

>>> from itertools import groupby
>>> sortkey = lambda i: i[0][0].lower()
>>> groups = groupby(sorted(dic.items(), key=sortkey), key=sortkey)
>>> result = dict(max(v, key=lambda i: i[1]) for k, v in groups)
>>> result
{('K1', 'K4'): 7.999999999999876, ('K2', 'K3'): 7.999999999999876, ('K3', 'S2'): 9.999999999999911, ('K4', 'S1'): 9.999999999999911, ('K5', 'K4'): 7.999999999999876, ('K6', 'S2'): 9.999999999999911}

NB: I used a sortkey when grouping because one of the keys in your example has a different case. If that was just a typo, you can omit it.

How to retrieve max key and corresponding value from the tuple in the dictionary based on the first argument of the tuple

2 Answers2