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from agate.aggregations.base import Aggregation
class First(Aggregation):
"""
Returns the first value that passes a test.
If the test is omitted, the aggregation will return the first value in the column.
If no values pass the test, the aggregation will raise an exception.
:param column_name:
The name of the column to check.
:param test:
A function that takes a value and returns `True` or `False`. Test may be
omitted when checking :class:`.Boolean` data.
"""
def __init__(self, column_name, test=None):
self._column_name = column_name
self._test = test
def get_aggregate_data_type(self, table):
return table.columns[self._column_name].data_type
def validate(self, table):
column = table.columns[self._column_name]
data = column.values()
if self._test is not None and len([d for d in data if self._test(d)]) == 0:
raise ValueError('No values pass the given test.')
def run(self, table):
column = table.columns[self._column_name]
data = column.values()
if self._test is None:
return data[0]
return next(d for d in data if self._test(d))
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