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