70 lines
2.1 KiB
Python
70 lines
2.1 KiB
Python
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"""
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Generators for interval graph.
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"""
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from collections.abc import Sequence
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import networkx as nx
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__all__ = ["interval_graph"]
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def interval_graph(intervals):
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""" Generates an interval graph for a list of intervals given.
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In graph theory, an interval graph is an undirected graph formed from a set
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of closed intervals on the real line, with a vertex for each interval
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and an edge between vertices whose intervals intersect.
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It is the intersection graph of the intervals.
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More information can be found at:
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https://en.wikipedia.org/wiki/Interval_graph
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Parameters
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----------
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intervals : a sequence of intervals, say (l, r) where l is the left end,
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and r is the right end of the closed interval.
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Returns
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-------
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G : networkx graph
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Examples
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--------
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>>> intervals = [(-2, 3), [1, 4], (2, 3), (4, 6)]
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>>> G = nx.interval_graph(intervals)
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>>> sorted(G.edges)
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[((-2, 3), (1, 4)), ((-2, 3), (2, 3)), ((1, 4), (2, 3)), ((1, 4), (4, 6))]
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Raises
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--------
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:exc:`TypeError`
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if `intervals` contains None or an element which is not
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collections.abc.Sequence or not a length of 2.
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:exc:`ValueError`
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if `intervals` contains an interval such that min1 > max1
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where min1,max1 = interval
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"""
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intervals = list(intervals)
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for interval in intervals:
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if not (isinstance(interval, Sequence) and len(interval) == 2):
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raise TypeError(
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"Each interval must have length 2, and be a "
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"collections.abc.Sequence such as tuple or list."
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)
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if interval[0] > interval[1]:
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raise ValueError(
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f"Interval must have lower value first. " f"Got {interval}"
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)
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graph = nx.Graph()
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tupled_intervals = [tuple(interval) for interval in intervals]
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graph.add_nodes_from(tupled_intervals)
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while tupled_intervals:
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min1, max1 = interval1 = tupled_intervals.pop()
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for interval2 in tupled_intervals:
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min2, max2 = interval2
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if max1 >= min2 and max2 >= min1:
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graph.add_edge(interval1, interval2)
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return graph
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