60 lines
1.9 KiB
Python
60 lines
1.9 KiB
Python
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#!/usr/bin/env python
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from agate.aggregations.has_nulls import HasNulls
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from agate.computations.base import Computation
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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 PercentChange(Computation):
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"""
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Calculate the percent difference between two columns.
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:param before_column_name:
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The name of a column containing the "before" :class:`.Number` values.
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:param after_column_name:
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The name of a column containing the "after" :class:`.Number` values.
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"""
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def __init__(self, before_column_name, after_column_name):
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self._before_column_name = before_column_name
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self._after_column_name = after_column_name
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def get_computed_data_type(self, table):
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return Number()
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def validate(self, table):
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before_column = table.columns[self._before_column_name]
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after_column = table.columns[self._after_column_name]
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if not isinstance(before_column.data_type, Number):
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raise DataTypeError('PercentChange before column must contain Number data.')
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if not isinstance(after_column.data_type, Number):
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raise DataTypeError('PercentChange after column must contain Number data.')
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if HasNulls(self._before_column_name).run(table):
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warn_null_calculation(self, before_column)
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if HasNulls(self._after_column_name).run(table):
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warn_null_calculation(self, after_column)
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def run(self, table):
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"""
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:returns:
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:class:`decimal.Decimal`
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"""
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new_column = []
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for row in table.rows:
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before = row[self._before_column_name]
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after = row[self._after_column_name]
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if before is not None and after is not None:
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new_column.append((after - before) / before * 100)
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else:
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new_column.append(None)
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return new_column
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