81 lines
2.3 KiB
Python
81 lines
2.3 KiB
Python
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#!/usr/bin/env python
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from agate.aggregations.base import Aggregation
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from agate.aggregations.has_nulls import HasNulls
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from agate.aggregations.mean import Mean
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from agate.data_types import Number
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from agate.exceptions import DataTypeError
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from agate.warns import warn_null_calculation
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class Variance(Aggregation):
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"""
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Calculate the sample variance of a column.
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For the population variance see :class:`.PopulationVariance`.
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:param column_name:
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The name of a column containing :class:`.Number` data.
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"""
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def __init__(self, column_name):
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self._column_name = column_name
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self._mean = Mean(column_name)
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def get_aggregate_data_type(self, table):
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return Number()
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def validate(self, table):
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column = table.columns[self._column_name]
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if not isinstance(column.data_type, Number):
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raise DataTypeError('Variance can only be applied to columns containing Number data.')
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has_nulls = HasNulls(self._column_name).run(table)
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if has_nulls:
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warn_null_calculation(self, column)
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def run(self, table):
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column = table.columns[self._column_name]
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data = column.values_without_nulls()
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mean = self._mean.run(table)
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return sum((n - mean) ** 2 for n in data) / (len(data) - 1)
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class PopulationVariance(Variance):
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"""
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Calculate the population variance of a column.
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For the sample variance see :class:`.Variance`.
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:param column_name:
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The name of a column containing :class:`.Number` data.
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"""
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def __init__(self, column_name):
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self._column_name = column_name
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self._mean = Mean(column_name)
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def get_aggregate_data_type(self, table):
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return Number()
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def validate(self, table):
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column = table.columns[self._column_name]
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if not isinstance(column.data_type, Number):
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raise DataTypeError('PopulationVariance can only be applied to columns containing Number data.')
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has_nulls = HasNulls(self._column_name).run(table)
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if has_nulls:
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warn_null_calculation(self, column)
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def run(self, table):
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column = table.columns[self._column_name]
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data = column.values_without_nulls()
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mean = self._mean.run(table)
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return sum((n - mean) ** 2 for n in data) / len(data)
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