# otp.agg.ob_snapshot_flat
### ob_snapshot_flat(running=False, bucket_interval=0, bucket_time='end', bucket_units=None, bucket_end_condition=None, end_condition_per_group=False, group_by=None, groups_to_display='all', max_levels=None, book_uncross_method=None, dq_events_that_clear_book=None, show_full_detail=False, max_initialization_days=1, state_key_max_inactivity_sec=None, size_max_fractional_digits=0, include_market_order_ticks=None)
Returns the snapshot for a specified number of book levels as a single tick
with multiple field groups corresponding to book levels.
* **Parameters:**
* **running** ([*bool*](https://docs.python.org/3/library/functions.html#bool) *,* *default=False*) --
See [Aggregation buckets guide](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`](../source/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`](../source/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'* *,* *'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()`](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.
* **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.
* **max_levels** ([*int*](https://docs.python.org/3/library/functions.html#int) *,* *default=None*) -- Number of order book levels (between 1 and 100_000) that need to be computed.
If empty, all levels will be computed.
* **book_uncross_method** (*Literal* *[* *'REMOVE_OLDER_CROSSED_LEVELS'* *]* *,* *default=None*) -- When set to "REMOVE_OLDER_CROSSED_LEVELS", all ask levels that have price lower or equal to
the price of a new bid tick get removed from the book, and all bid levels that have price higher or equal
to the price of a new ask tick get removed from the book.
* **dq_events_that_clear_book** (*List* *[*[*str*](https://docs.python.org/3/library/stdtypes.html#str) *]* *,* *default=None*) -- A list of names of data quality events arrival of which should clear the order book.
* **show_full_detail** ([*bool*](https://docs.python.org/3/library/functions.html#bool) *,* *default=False*) -- When set to "true" and if the state key of the input ticks consists of some fields besides PRICE,
output ticks will contain all fields from the input ticks for each price level.
When set to "false" only PRICE, UPDATE_TIME, SIZE, LEVEL, and BUY_SELL_FLAG fields will be populated.
Note: setting this flag to "true" has no effect on a time series that does not have a state key.
* **max_initialization_days** ([*int*](https://docs.python.org/3/library/functions.html#int) *,* *default=1*) -- This parameter specifies how many days back book event processors should go in order to find
the latest full state of the book.
The query will not go back resulting number of days if it finds initial book state earlier.
When book event processors are used after VIRTUAL_OB EP, this parameter should be set to 0.
When set, this parameter takes precedence over the configuration parameter BOOKS.MAX_INITIALIZATION_DAYS.
* **state_key_max_inactivity_sec** ([*int*](https://docs.python.org/3/library/functions.html#int) *,* *default=None*) -- If set, specifies in how many seconds after it was added
a given state key should be automatically removed from the book.
* **size_max_fractional_digits** ([*int*](https://docs.python.org/3/library/functions.html#int) *,* *default=0*) -- Specifies maximum number of digits after dot in SIZE, if SIZE can be fractional.
* **include_market_order_ticks** ([*bool*](https://docs.python.org/3/library/functions.html#bool) *,* *default=None*) --
If set, market order ticks (they have price NaN) are included into the order book,
and are at the order book's top level.
> Default is False.
### Examples
```pycon
>>> data = otp.DataSource(db='CME_SAMPLE', tick_type='PRL_FULL', symbols=r'NQ\H24')
>>> data = otp.agg.ob_snapshot_flat(max_levels=3).apply(data)
>>> otp.run(data, start=otp.dt(2024, 2, 1, 10), end=otp.dt(2024, 2, 1, 10))
Time BID_PRICE1 BID_SIZE1 BID_UPDATE_TIME1 ASK_PRICE1 ASK_SIZE1 ...
0 2024-02-01 10:00:00 17351.25 1 2024-02-01 09:59:59.867609851 17351.75 1 ...
```
#### SEE ALSO
[`onetick.py.ObSnapshotFlat()`](../sources/order_book/ob_snapshot_flat.md#onetick.py.ObSnapshotFlat)
**OB_SNAPSHOT_FLAT** OneTick event processor