# otp.Source.first #### Source.first(n=1, running=False, bucket_interval=0, bucket_time='end', bucket_units=None, bucket_end_condition=None, end_condition_per_group=False, boundary_tick_bucket='new', group_by=None, groups_to_display='all', keep_timestamp=True, default_tick=None) Select the first **n** ticks * **Parameters:** * **n** ([*int*](https://docs.python.org/3/library/functions.html#int) *,* *default=1*) -- Number of ticks to output * **running** ([*bool*](https://docs.python.org/3/library/functions.html#bool) *,* *default=False*) -- See [Aggregation buckets guide](../aggregations/root.md#buckets-guide) to see examples of how this parameter works. Specifies if the aggregation will be calculated as a sliding window. `running` and `bucket_interval` parameters determines when new buckets are created. * `running` = True aggregation will be calculated in a sliding window. * `bucket_interval` = N (N > 0) Window size will be N. Output tick will be generated when tick "enter" window (**arrival event**) and when "exit" window (**exit event**) * `bucket_interval` = 0 Left boundary of window will be set to query start time. For each tick aggregation will be calculated in the interval [start_time; tick_t] from query start time to the tick's timestamp (inclusive). * `running` = False (default) buckets partition the [query start time, query end time) interval into non-overlapping intervals of size `bucket_interval` (with the last interval possibly of a smaller size). If `bucket_interval` is set to **0** a single bucket for the entire interval is created. Note that in non-running mode OneTick unconditionally divides the whole time interval into specified number of buckets. It means that you will always get this specified number of ticks in the result, even if you have less ticks in the input data. Default: False * **bucket_interval** (int or float or [`Operation`](../operation/root.md#onetick.py.Operation) or [`OnetickParameter`](../misc/param.md#onetick.py.core.column_operations.base.OnetickParameter) or [`symbol parameter`](Symbol.md#onetick.py.core._source.symbol.SymbolType.__getitem__) or [datetime offset object](../datetime/offsets/root.md#id1), default=0) -- Determines the length of each bucket (units depends on `bucket_units`). If [`Operation`](../operation/root.md#onetick.py.Operation) of bool type is passed, acts as `bucket_end_condition`. Bucket interval can also be set as a *float* value if `bucket_units` is set to *seconds*. Note that values less than 0.001 (1 millisecond) are not supported. Bucket interval can be set via some of the [datetime offset objects](../datetime/offsets/root.md#id1): [`otp.Milli`](../datetime/offsets/milli.md#onetick.py.Milli), [`otp.Second`](../datetime/offsets/second.md#onetick.py.Second), [`otp.Minute`](../datetime/offsets/minute.md#onetick.py.Minute), [`otp.Hour`](../datetime/offsets/hour.md#onetick.py.Hour), [`otp.Day`](../datetime/offsets/day.md#onetick.py.Day), [`otp.Month`](../datetime/offsets/month.md#onetick.py.Month). In this case you could omit setting `bucket_units` parameter. Bucket interval can also be set with integer [`OnetickParameter`](../misc/param.md#onetick.py.core.column_operations.base.OnetickParameter) or [`symbol parameter`](Symbol.md#onetick.py.core._source.symbol.SymbolType.__getitem__). * **bucket_time** (*Literal* *[* *'start'* *,* *'end'* *]* *,* *default=end*) -- Control output timestamp. * **start** the timestamp assigned to the bucket is the start time of the bucket. * **end** the timestamp assigned to the bucket is the end time of the bucket. * **bucket_units** (*Optional* *[**Literal* *[* *'seconds'* *,* *'ticks'* *,* *'days'* *,* *'months'* *,* *'flexible'* *]* *]* *,* *default=None*) -- Set bucket interval units. By default, if `bucket_units` and `bucket_end_condition` not specified, set to **seconds**. If `bucket_end_condition` specified, then `bucket_units` set to **flexible**. If set to **flexible** then `bucket_end_condition` must be set. Note that **seconds** bucket unit doesn't take into account daylight-saving time of the timezone, so you may not get expected results when using, for example, 24 \* 60 \* 60 seconds as bucket interval. In such case use **days** bucket unit instead. See example in [`onetick.py.agg.sum()`](../aggregations/sum.md#onetick.py.agg.sum). * **bucket_end_condition** (*condition* *,* *default=None*) -- An expression that is evaluated on every tick. If it evaluates to "True", then a new bucket is created. This parameter is only used if `bucket_units` is set to "flexible". Also can be set via `bucket_interval` parameter by passing [`Operation`](../operation/root.md#onetick.py.Operation) object. * **end_condition_per_group** ([*bool*](https://docs.python.org/3/library/functions.html#bool) *,* *default=False*) -- Controls application of `bucket_end_condition` in groups. * `end_condition_per_group` = True `bucket_end_condition` is applied only to the group defined by `group_by` * `end_condition_per_group` = False `bucket_end_condition` applied across all groups This parameter is only used if `bucket_units` is set to "flexible". When set to True, applies to all bucketing conditions. Useful, for example, if you need to specify `group_by`, and you want to group items first, and create buckets after that. * **boundary_tick_bucket** (*Literal* *[* *'new'* *,* *'previous'* *]* *,* *default=new*) -- Controls boundary tick ownership. * **previous** A tick on which `bucket_end_condition` evaluates to "true" belongs to the bucket being closed. * **new** tick belongs to the new bucket. This parameter is only used if `bucket_units` is set to "flexible" * **group_by** ([*list*](https://docs.python.org/3/library/stdtypes.html#list) *,* [*str*](https://docs.python.org/3/library/stdtypes.html#str) *or* *expression* *,* *default=None*) -- When specified, each bucket is broken further into additional sub-buckets based on specified field values. If [`Operation`](../operation/root.md#onetick.py.Operation) is used then GROUP_{i} column is added. Where i is index in group_by list. For example, if Operation is the only element in `group_by` list then GROUP_0 field will be added. * **groups_to_display** (*Literal* *[* *'all'* *,* *'previous'* *]* *,* *default=all*) -- Specifies for which sub-buckets (groups) ticks should be shown for each bucket interval. By default **all** groups are shown at the end of each bucket interval. If this parameter is set to **event_in_last_bucket**, only the groups that received at least one tick within a given bucket interval are shown. * **keep_timestamp** ([*bool*](https://docs.python.org/3/library/functions.html#bool) *,* *default=True*) -- If True, timestamps of the output ticks are the same as timestamps of the original ticks. Otherwise, timestamps of the output ticks are determined by bucket_time, and original timestamps are put in the TICK_TIME field. * **default_tick** (*Optional* *[*[*dict*](https://docs.python.org/3/library/stdtypes.html#dict) *]* *,* *default=None*) -- Mapping of input stream field names to some values. When set, exactly one tick with specified default values will be created for each empty bucket. If default value is specified as `None`, then fields are initialized to the corresponding "zero" values: 0 for integer types, NaN for doubles, empty string for string types, etc. * **Return type:** [Source](root.md#onetick.py.Source) ### Examples Get first tick: ```pycon >>> data = otp.Ticks(X=[1, 2, 3, 4]) >>> data = data.first() >>> otp.run(data) Time X 0 2003-12-01 1 ``` Get first tick each day: ```pycon >>> data = otp.Ticks(X=[1, 2, 3, 4], offset=[otp.Day(0), otp.Day(0), otp.Day(2), otp.Day(2)]) >>> data = data.first(bucket_interval=1, bucket_units='days', bucket_time='start') >>> otp.run(data) Time X 0 2003-12-01 1 1 2003-12-03 3 ``` Get first tick each day and set tick value for empty buckets: ```pycon >>> data = otp.Ticks(X=[1, 2, 3, 4], offset=[otp.Day(0), otp.Day(0), otp.Day(2), otp.Day(2)]) >>> data = data.first(bucket_interval=1, bucket_units='days', bucket_time='start', default_tick={'X': -1}) >>> otp.run(data) Time X 0 2003-12-01 1 1 2003-12-02 -1 2 2003-12-03 3 ``` #### SEE ALSO **FIRST_TICK** OneTick event processor