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from collections import OrderedDict |
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def expand_tuples(L): |
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""" |
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>>> from sympy.multipledispatch.utils import expand_tuples |
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>>> expand_tuples([1, (2, 3)]) |
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[(1, 2), (1, 3)] |
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>>> expand_tuples([1, 2]) |
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[(1, 2)] |
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""" |
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if not L: |
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return [()] |
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elif not isinstance(L[0], tuple): |
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rest = expand_tuples(L[1:]) |
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return [(L[0],) + t for t in rest] |
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else: |
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rest = expand_tuples(L[1:]) |
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return [(item,) + t for t in rest for item in L[0]] |
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def _toposort(edges): |
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""" Topological sort algorithm by Kahn [1] - O(nodes + vertices) |
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inputs: |
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edges - a dict of the form {a: {b, c}} where b and c depend on a |
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outputs: |
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L - an ordered list of nodes that satisfy the dependencies of edges |
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>>> from sympy.multipledispatch.utils import _toposort |
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>>> _toposort({1: (2, 3), 2: (3, )}) |
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[1, 2, 3] |
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Closely follows the wikipedia page [2] |
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[1] Kahn, Arthur B. (1962), "Topological sorting of large networks", |
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Communications of the ACM |
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[2] https://en.wikipedia.org/wiki/Toposort#Algorithms |
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""" |
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incoming_edges = reverse_dict(edges) |
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incoming_edges = {k: set(val) for k, val in incoming_edges.items()} |
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S = OrderedDict.fromkeys(v for v in edges if v not in incoming_edges) |
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L = [] |
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while S: |
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n, _ = S.popitem() |
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L.append(n) |
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for m in edges.get(n, ()): |
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assert n in incoming_edges[m] |
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incoming_edges[m].remove(n) |
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if not incoming_edges[m]: |
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S[m] = None |
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if any(incoming_edges.get(v, None) for v in edges): |
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raise ValueError("Input has cycles") |
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return L |
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def reverse_dict(d): |
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"""Reverses direction of dependence dict |
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>>> d = {'a': (1, 2), 'b': (2, 3), 'c':()} |
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>>> reverse_dict(d) # doctest: +SKIP |
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{1: ('a',), 2: ('a', 'b'), 3: ('b',)} |
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:note: dict order are not deterministic. As we iterate on the |
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input dict, it make the output of this function depend on the |
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dict order. So this function output order should be considered |
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as undeterministic. |
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""" |
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result = {} |
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for key in d: |
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for val in d[key]: |
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result[val] = result.get(val, ()) + (key, ) |
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return result |
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def groupby(func, seq): |
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""" Group a collection by a key function |
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>>> from sympy.multipledispatch.utils import groupby |
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>>> names = ['Alice', 'Bob', 'Charlie', 'Dan', 'Edith', 'Frank'] |
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>>> groupby(len, names) # doctest: +SKIP |
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{3: ['Bob', 'Dan'], 5: ['Alice', 'Edith', 'Frank'], 7: ['Charlie']} |
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>>> iseven = lambda x: x % 2 == 0 |
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>>> groupby(iseven, [1, 2, 3, 4, 5, 6, 7, 8]) # doctest: +SKIP |
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{False: [1, 3, 5, 7], True: [2, 4, 6, 8]} |
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See Also: |
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``countby`` |
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""" |
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d = {} |
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for item in seq: |
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key = func(item) |
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if key not in d: |
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d[key] = [] |
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d[key].append(item) |
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return d |
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