How to generate all combination from values in dict of lists in Python

Question

I would like to generate all combinations of values which are in lists indexed in a dict:

{'A':['D','E'],'B':['F','G','H'],'C':['I','J']}

Each time, one item of each dict entry would be picked and combined to items from other keys, so I have:

['D','F','I']
['D','F','J']
['D','G','I']
['D','G','J']
['D','H','I']
...
['E','H','J']

I know there is a something to generate combinations of items in list in itertools but I don't think I can use it here since I have different "pools" of values.

Is there any existing solution to do this, or how should I proceed to do it myself, I am quite stuck with this nested structure.

Anima

Then you should try to write code to do so, and come back if you have problems. – Possessory

itertools.product(*yourdict.values()) – Devlin

dictionaries are not ordered! please clarify. – Zellner

I tried to write code but I got stuck, I am actually looking for a existing solution not to waste my time on this ... I don't understand why you say dictionnaries are not ordered, I know that and this has nothing to do with my problem, I want combinations, not permutations. @Devlin : Thank you I'm trying it. – Anima

You assumed an order. Why is D the first letter, and not... say F? – Zellner

You assumed this ... I could have written F before D ... this doesn't change the problem ... Btw, itertools.product didn't work – Anima

Of course I did. Your description wasn't clear. BTW, why do you use a list then? Use a set. – Zellner

Answer 1

import itertools as it

my_dict={'A':['D','E'],'B':['F','G','H'],'C':['I','J']}
allNames = sorted(my_dict)
combinations = it.product(*(my_dict[Name] for Name in allNames))
print(list(combinations))

Which prints:

[('D', 'F', 'I'), ('D', 'F', 'J'), ('D', 'G', 'I'), ('D', 'G', 'J'), ('D', 'H', 'I'), ('D', 'H', 'J'), ('E', 'F', 'I'), ('E', 'F', 'J'), ('E', 'G', 'I'), ('E', 'G', 'J'), ('E', 'H', 'I'), ('E', 'H', 'J')]

Artistry

need to sort the dict first otherwise values can be associated with the wrong key – Ensoll

Answer 2

If you want to keep the key:value in the permutations you can use:

import itertools
keys, values = zip(*my_dict.items())
permutations_dicts = [dict(zip(keys, v)) for v in itertools.product(*values)]

this will provide you a list of dicts with the permutations:

print(permutations_dicts)
[{'A':'D', 'B':'F', 'C':'I'}, 
 {'A':'D', 'B':'F', 'C':'J'},
 ...
 ]

Disclaimer: not exactly what the OP was asking, but google send me here looking for that. If you want to obtain what OP is asking you should just remove the dict part in the list comprehension, i.e.

permutations_dicts = [v for v in itertools.product(*values)]

Perigon

Answer 3

ParameterGrid from scikit-learn creates a generator. Each for loop iteration will give you a dictionary containing the current parameter combination.

from sklearn.model_selection import ParameterGrid

params = {'A':['D','E'],'B':['F','G','H'],'C':['I','J']}
param_grid = ParameterGrid(params)
for dict_ in param_grid:
    print(dict_)
    

# output
{'A': 'D', 'B': 'F', 'C': 'I'}
...

Breastbone

This is neat if you already are working in an environment with scikit-learn. The itertools is part of the standard library, though. – Optimize

This was the best answer in my case, thank you. – Inexact

Answer 4

as a complement, here is a 3-liner that does it in pure python so that you get the idea, but itertools is indeed more efficient.

res = [[]]
for _, vals in my_dict.items():
    res = [x+[y] for x in res for y in vals]
print(res)

Threequarter

Answer 5

from itertools import combinations

a=['I1','I2','I3','I4','I5']

list(combinations(a,2))

The output will be:

[('I1', 'I2'),
 ('I1', 'I3'),
 ('I1', 'I4'),
 ('I1', 'I5'),
 ('I2', 'I3'),
 ('I2', 'I4'),
 ('I2', 'I5'),
 ('I3', 'I4'),
 ('I3', 'I5'),
 ('I4', 'I5')]

Plumbiferous