|
|
|
|
|
|
|
|
|
|
|
|
|
|
| """
|
| Tools for comparing ranked lists.
|
| """
|
|
|
|
|
| def _rank_dists(ranks1, ranks2):
|
| """Finds the difference between the values in ranks1 and ranks2 for keys
|
| present in both dicts. If the arguments are not dicts, they are converted
|
| from (key, rank) sequences.
|
| """
|
| ranks1 = dict(ranks1)
|
| ranks2 = dict(ranks2)
|
| for k in ranks1:
|
| try:
|
| yield k, ranks1[k] - ranks2[k]
|
| except KeyError:
|
| pass
|
|
|
|
|
| def spearman_correlation(ranks1, ranks2):
|
| """Returns the Spearman correlation coefficient for two rankings, which
|
| should be dicts or sequences of (key, rank). The coefficient ranges from
|
| -1.0 (ranks are opposite) to 1.0 (ranks are identical), and is only
|
| calculated for keys in both rankings (for meaningful results, remove keys
|
| present in only one list before ranking)."""
|
| n = 0
|
| res = 0
|
| for k, d in _rank_dists(ranks1, ranks2):
|
| res += d * d
|
| n += 1
|
| try:
|
| return 1 - (6 * res / (n * (n * n - 1)))
|
| except ZeroDivisionError:
|
|
|
| return 0.0
|
|
|
|
|
| def ranks_from_sequence(seq):
|
| """Given a sequence, yields each element with an increasing rank, suitable
|
| for use as an argument to ``spearman_correlation``.
|
| """
|
| return ((k, i) for i, k in enumerate(seq))
|
|
|
|
|
| def ranks_from_scores(scores, rank_gap=1e-15):
|
| """Given a sequence of (key, score) tuples, yields each key with an
|
| increasing rank, tying with previous key's rank if the difference between
|
| their scores is less than rank_gap. Suitable for use as an argument to
|
| ``spearman_correlation``.
|
| """
|
| prev_score = None
|
| rank = 0
|
| for i, (key, score) in enumerate(scores):
|
| try:
|
| if abs(score - prev_score) > rank_gap:
|
| rank = i
|
| except TypeError:
|
| pass
|
|
|
| yield key, rank
|
| prev_score = score
|
|
|
