# otp.Source._\_getitem_\_ #### Source.\_\_getitem_\_(item) 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`](https://docs.pip.distribution.sol.onetick.com/api/operation/root.html.md#onetick.py.Operation), [`eval()`](https://docs.pip.distribution.sol.onetick.com/api/misc/eval.html.md#onetick.py.eval), list of str) -- - `str` is to access column by name or columns specified by regex. - `Operation` to express filter condition. - `otp.eval` to express filter condition based on external query - `list[str]` select subset of specified columns or columns specified in regexes. - `slice[list[str]::]` set order of columns - `slice[tuple[str, type]::]` type defaulting - `slice[:]` alias to [`Source.copy()`](https://docs.pip.distribution.sol.onetick.com/api/source/self/copy.html.md#onetick.py.Source.copy) - `slice[int:int:int]` select ticks the same way as elements in python lists * **self** ([*Source*](https://docs.pip.distribution.sol.onetick.com/api/source/root.html.md#onetick.py.Source)) * **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](https://docs.pip.distribution.sol.onetick.com/api/operation/root.html.md#onetick.py.Column), [Source](https://docs.pip.distribution.sol.onetick.com/api/source/root.html.md#onetick.py.Source) or [tuple](https://docs.python.org/3/builtins/stdtypes.html#tuple) of Sources ### Examples Access to the X column: add Y based on X ```pycon >>> 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: ```pycon >>> 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). ```pycon >>> 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: ```pycon >>> 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: ```pycon >>> data=otp.Tick(Y=1, X=2, Z=3) >>> otp.run(data) Time Y X Z 0 2003-12-01 1 2 3 >>> data = data[['X', 'Y']:] >>> otp.run(data) Time X Y Z 0 2003-12-01 2 1 3 ``` Slice can be used as short-cut for [`Source.copy()`](https://docs.pip.distribution.sol.onetick.com/api/source/self/copy.html.md#onetick.py.Source.copy): ```pycon >>> data[:] ``` Slices can use integers. In this case ticks are selected the same way as elements in python lists. ```pycon >>> data = otp.Ticks({'A': [1, 2, 3, 4, 5]}) ``` Select first 3 ticks: ```pycon >>> otp.run(data[:3]) Time A 0 2003-12-01 00:00:00.000 1 1 2003-12-01 00:00:00.001 2 2 2003-12-01 00:00:00.002 3 ``` Skip first 3 ticks: ```pycon >>> otp.run(data[3:]) Time A 0 2003-12-01 00:00:00.003 4 1 2003-12-01 00:00:00.004 5 ``` Select last 3 ticks: ```pycon >>> otp.run(data[-3:]) Time A 0 2003-12-01 00:00:00.002 3 1 2003-12-01 00:00:00.003 4 2 2003-12-01 00:00:00.004 5 ``` Skip last 3 ticks: ```pycon >>> otp.run(data[:-3]) Time A 0 2003-12-01 00:00:00.000 1 1 2003-12-01 00:00:00.001 2 ``` Skip first and last tick: ```pycon >>> otp.run(data[1:-1]) Time A 0 2003-12-01 00:00:00.001 2 1 2003-12-01 00:00:00.002 3 2 2003-12-01 00:00:00.003 4 ``` Select every second tick: ```pycon >>> otp.run(data[::2]) Time A 0 2003-12-01 00:00:00.000 1 1 2003-12-01 00:00:00.002 3 2 2003-12-01 00:00:00.004 5 ``` Select every second tick, not including first and last tick: ```pycon >>> otp.run(data[1:-1:2]) Time A 0 2003-12-01 00:00:00.001 2 1 2003-12-01 00:00:00.003 4 ``` Regular expressions can be used to select fields too: ```pycon >>> data = otp.Tick(A=1, AA=2, AB=3, B=4, BB=5, BA=6) >>> otp.run(data['A.*']) Time A AA AB BA 0 2003-12-01 1 2 3 6 ``` Note that by default pattern is matched in any position of the string. Use characters ^ and $ to specify start and end of the string: ```pycon >>> otp.run(data['^A']) Time A AA AB 0 2003-12-01 1 2 3 ``` Several regular expressions can be specified too: ```pycon >>> otp.run(data[['^A+$', '^B+$']]) Time A AA B BB 0 2003-12-01 1 2 4 5 ``` #### SEE ALSO [`Source.table()`](https://docs.pip.distribution.sol.onetick.com/api/source/fields/table.html.md#onetick.py.Source.table): another and more generic way to select subset of specified columns
**PASSTHROUGH** OneTick event processor
**WHERE_CLAUSE** OneTick event processor