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from agate.aggregations import Aggregation
from agate.aggregations.has_nulls import HasNulls
from agate.aggregations.variance import PopulationVariance, Variance
from agate.data_types import Number
from agate.exceptions import DataTypeError
from agate.warns import warn_null_calculation
class StDev(Aggregation):
"""
Calculate the sample standard of deviation of a column.
For the population standard of deviation see :class:`.PopulationStDev`.
:param column_name:
The name of a column containing :class:`.Number` data.
"""
def __init__(self, column_name):
self._column_name = column_name
self._variance = Variance(column_name)
def get_aggregate_data_type(self, table):
return Number()
def validate(self, table):
column = table.columns[self._column_name]
if not isinstance(column.data_type, Number):
raise DataTypeError('StDev can only be applied to columns containing Number data.')
has_nulls = HasNulls(self._column_name).run(table)
if has_nulls:
warn_null_calculation(self, column)
def run(self, table):
variance = self._variance.run(table)
if variance is not None:
return variance.sqrt()
class PopulationStDev(StDev):
"""
Calculate the population standard of deviation of a column.
For the sample standard of deviation see :class:`.StDev`.
:param column_name:
The name of a column containing :class:`.Number` data.
"""
def __init__(self, column_name):
self._column_name = column_name
self._population_variance = PopulationVariance(column_name)
def get_aggregate_data_type(self, table):
return Number()
def validate(self, table):
column = table.columns[self._column_name]
if not isinstance(column.data_type, Number):
raise DataTypeError('PopulationStDev can only be applied to columns containing Number data.')
has_nulls = HasNulls(self._column_name).run(table)
if has_nulls:
warn_null_calculation(self, column)
def run(self, table):
variance = self._population_variance.run(table)
if variance is not None:
return variance.sqrt()
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