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from decimal import Decimal
from functools import cmp_to_key
from agate.computations.base import Computation
from agate.data_types import Number
class Rank(Computation):
"""
Calculate rank order of the values in a column.
Uses the "competition" ranking method: if there are four values and the
middle two are tied, then the output will be `[1, 2, 2, 4]`.
Null values will always be ranked last.
:param column_name:
The name of the column to rank.
:param comparer:
An optional comparison function. If not specified ranking will be
ascending, with nulls ranked last.
:param reverse:
Reverse sort order before ranking.
"""
def __init__(self, column_name, comparer=None, reverse=None):
self._column_name = column_name
self._comparer = comparer
self._reverse = reverse
def get_computed_data_type(self, table):
return Number()
def run(self, table):
"""
:returns:
:class:`int`
"""
column = table.columns[self._column_name]
if self._comparer:
data_sorted = sorted(column.values(), key=cmp_to_key(self._comparer))
else:
data_sorted = column.values_sorted()
if self._reverse:
data_sorted.reverse()
ranks = {}
rank = 0
for c in data_sorted:
rank += 1
if c in ranks:
continue
ranks[c] = Decimal(rank)
new_column = []
for row in table.rows:
new_column.append(ranks[row[self._column_name]])
return new_column
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