combinations_from_relations¶

iteration_utilities.
combinations_from_relations
(dictionary, r)¶ Yield combinations where only one item (or None) of each equivalence class is present.
Parameters: dictionary :
dict
with iterable values or convertible to one.A dictionary defining the equivalence classes, each key should contain all equivalent items as it’s value.
Warning
Each
value
in the dictionary must be iterable.Note
If the dictionary isn’t ordered then the order in the combinations and their order of appearance is notdeterministic.
Note
If the dictionary isn’t
dict
like it will be converted to ancollections.OrderedDict
.r :
int
or None, optionalThe number of combinations, if
None
it defaults to the length of the dictionary.Returns: combinations : generator
The combinations from the dictionary.
Examples
In general the
collections.OrderedDict
should be used to call the function. But it will also be automatically converted to one if one inserts an iterable that is convertible to a dict:>>> from iteration_utilities import combinations_from_relations >>> classes = [('a', [1, 2]), ('b', [3, 4]), ('c', [5, 6])] >>> for comb in combinations_from_relations(classes, 2): ... print(comb) (1, 3) (1, 4) (2, 3) (2, 4) (1, 5) (1, 6) (2, 5) (2, 6) (3, 5) (3, 6) (4, 5) (4, 6)
This is equivalent to creating the
collections.OrderedDict
manually:>>> from collections import OrderedDict >>> odct = OrderedDict(classes) >>> for comb in combinations_from_relations(odct, 3): ... print(comb) (1, 3, 5) (1, 3, 6) (1, 4, 5) (1, 4, 6) (2, 3, 5) (2, 3, 6) (2, 4, 5) (2, 4, 6)