45 lines
1.3 KiB
Python
45 lines
1.3 KiB
Python
#!/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.median import Median
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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.utils import median
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from agate.warns import warn_null_calculation
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class MAD(Aggregation):
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"""
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Calculate the `median absolute deviation <http://en.wikipedia.org/wiki/Median_absolute_deviation>`_
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of a column.
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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._median = Median(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('MAD 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_sorted()
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m = self._median.run(table)
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return median(tuple(abs(n - m) for n in data))
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