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):
return self._variance.run(table).sqrt()
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()
def __init__(self, column_name):
self._column_name = column_name
self._variance = Variance(column_name)
def __init__(self, column_name):
self._column_name = column_name
self._variance = Variance(column_name)