otp.Source.getitem#

Source.__getitem__(item)[source]#

Allows to express multiple things:

access a field by name
filter ticks by condition
select subset of fields
set order of fields

Parameters

item (str, Operation, eval(), List[str]) –

str is to access column.
Operation to express filter condition.
otp.eval to express filter condition based on external query
List[str] select subset of specified columns
slice[List[str]::] set order of columns
slice[Tuple[str, Type]::] type defaulting
slice[:] alias to Source.copy()

Returns

Column if column name was specified.
Two sources if filtering expression or eval was provided: the first one is for ticks that pass condition and the second one that do not.

Return type

Column, Source or tuple of Sources

Examples

Access to the X column: add Y based on X

>>> data = otp.Ticks(X=[1, 2, 3])
>>> data['Y'] = data['X'] * 2
>>> otp.run(data)
                     Time  X  Y
0 2003-12-01 00:00:00.000  1  2
1 2003-12-01 00:00:00.001  2  4
2 2003-12-01 00:00:00.002  3  6

Filtering based on expression

>>> data = otp.Ticks(X=[1, 2, 3])
>>> data_more, data_less = data[(data['X'] > 2)]
>>> otp.run(data_more)
                     Time  X
0 2003-12-01 00:00:00.002  3
>>> otp.run(data_less)
                     Time  X
0 2003-12-01 00:00:00.000  1
1 2003-12-01 00:00:00.001  2

Filtering based on the result of another query. Another query should have only one tick as a result with only one field (whatever it names).

>>> exp_to_select = otp.Ticks(WHERE=['X > 2'])
>>> data = otp.Ticks(X=[1, 2, 3], Y=['a', 'b', 'c'], Z=[.4, .3, .1])
>>> data, _ = data[otp.eval(exp_to_select)]
>>> otp.run(data)
                     Time  X  Y    Z
0 2003-12-01 00:00:00.002  3  c  0.1

Select subset of specified columns

>>> data = otp.Ticks(X=[1, 2, 3], Y=['a', 'b', 'c'], Z=[.4, .3, .1])
>>> data = data[['X', 'Z']]
>>> otp.run(data)
                     Time  X    Z
0 2003-12-01 00:00:00.000  1  0.4
1 2003-12-01 00:00:00.001  2  0.3
2 2003-12-01 00:00:00.002  3  0.1

Slice with list will keep all columns, but change order:

>>> data=otp.Tick(Y=1, X=2, Z=3)
>>> data()
        Time  Y  X  Z
0 2003-12-01  1  2  3
>>> data = data[['X', 'Y']:]
>>> data()
        Time  X  Y  Z
0 2003-12-01  2  1  3

Slice can be used as short-cut for Source.copy():

>>> data[:] 
<onetick.py.sources.Tick object at ...>

otp.Source.__getitem__#

otp.Source.getitem#