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Prepare private _rank() function to be made public. #96372

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Merged
rhettinger merged 2 commits into from
Aug 29, 2022
Merged

Prepare private _rank() function to be made public. #96372

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8e390c2
Prepare private _rank() function to be made public.
rhettinger Aug 29, 2022
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rhettinger Aug 29, 2022
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20 changes: 15 additions & 5 deletions Lib/statistics.py
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Original file line number Diff line number Diff line change
Expand Up @@ -355,7 +355,8 @@ def _fail_neg(values, errmsg='negative value'):
raise StatisticsError(errmsg)
yield x

def _rank(data, /, *, key=None, reverse=False, ties='average') -> list[float]:

def _rank(data, /, *, key=None, reverse=False, ties='average', start=1) -> list[float]:
"""Rank order a dataset. The lowest value has rank 1.

Ties are averaged so that equal values receive the same rank:
Expand All @@ -369,14 +370,22 @@ def _rank(data, /, *, key=None, reverse=False, ties='average') -> list[float]:
>>> _rank([3.5, 5.0, 3.5, 2.0, 6.0, 1.0])
[3.5, 5.0, 3.5, 2.0, 6.0, 1.0]

It is possible to rank the data in reverse order so that
the highest value has rank 1. Also, a key-function can
extract the field to be ranked:
It is possible to rank the data in reverse order so that the
highest value has rank 1. Also, a key-function can extract
the field to be ranked:

>>> goals = [('eagles', 45), ('bears', 48), ('lions', 44)]
>>> _rank(goals, key=itemgetter(1), reverse=True)
[2.0, 1.0, 3.0]

Ranks are conventionally numbered starting from one; however,
setting *start* to zero allow the ranks to be used as array indices:

>>> prize = ['Gold', 'Silver', 'Bronze', 'Certificate']
>>> scores = [8.1, 7.3, 9.4, 8.3]
>>> [prize[int(i)] for i in _rank(scores, start=0, reverse=True)]
['Bronze', 'Certificate', 'Gold', 'Silver']

"""
# If this function becomes public at some point, more thought
# needs to be given to the signature. A list of ints is
Expand All @@ -389,7 +398,7 @@ def _rank(data, /, *, key=None, reverse=False, ties='average') -> list[float]:
if key is not None:
data = map(key, data)
val_pos = sorted(zip(data, count()), reverse=reverse)
i = 0 # To rank starting at 0 instead of 1, set i = -1.
i = start - 1
result = [0] * len(val_pos)
for _, g in groupby(val_pos, key=itemgetter(0)):
group = list(g)
Expand All @@ -400,6 +409,7 @@ def _rank(data, /, *, key=None, reverse=False, ties='average') -> list[float]:
i += size
return result


def _integer_sqrt_of_frac_rto(n: int, m: int) -> int:
"""Square root of n/m, rounded to the nearest integer using round-to-odd."""
# Reference: https://www.lri.fr/~melquion/doc/05-imacs17_1-expose.pdf
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