1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
|
from agate.aggregations.has_nulls import HasNulls
from agate.computations.base import Computation
from agate.data_types import Date, DateTime, Number, TimeDelta
from agate.exceptions import DataTypeError
from agate.warns import warn_null_calculation
class Change(Computation):
"""
Calculate the difference between two columns.
This calculation can be applied to :class:`.Number` columns to calculate
numbers. It can also be applied to :class:`.Date`, :class:`.DateTime`, and
:class:`.TimeDelta` columns to calculate time deltas.
:param before_column_name:
The name of a column containing the "before" values.
:param after_column_name:
The name of a column containing the "after" values.
"""
def __init__(self, before_column_name, after_column_name):
self._before_column_name = before_column_name
self._after_column_name = after_column_name
def get_computed_data_type(self, table):
before_column = table.columns[self._before_column_name]
if isinstance(before_column.data_type, (Date, DateTime, TimeDelta)):
return TimeDelta()
if isinstance(before_column.data_type, Number):
return Number()
def validate(self, table):
before_column = table.columns[self._before_column_name]
after_column = table.columns[self._after_column_name]
for data_type in (Number, Date, DateTime, TimeDelta):
if isinstance(before_column.data_type, data_type):
if not isinstance(after_column.data_type, data_type):
raise DataTypeError('Specified columns must be of the same type')
if HasNulls(self._before_column_name).run(table):
warn_null_calculation(self, before_column)
if HasNulls(self._after_column_name).run(table):
warn_null_calculation(self, after_column)
return
raise DataTypeError('Change before and after columns must both contain data that is one of: '
'Number, Date, DateTime or TimeDelta.')
def run(self, table):
new_column = []
for row in table.rows:
before = row[self._before_column_name]
after = row[self._after_column_name]
if before is not None and after is not None:
new_column.append(after - before)
else:
new_column.append(None)
return new_column
|
