use_row_list
use_row_list
lets you use the data of the first row of a table as a list. This is useful when you want to listen to an updating table and use the data in your component.
Example
from deephaven import time_table, ui
@ui.component
def ui_table_row_list(table):
row_list = ui.use_row_list(table)
if row_list == ():
return ui.heading("No data yet.")
return ui.heading(f"The row list is {row_list}. Value of X is {row_list[1]}.")
table_row_list = ui_table_row_list(time_table("PT1s").update("x=i").reverse())
In the above example, ui_table_row_list
is a component that listens to a table and displays the first row of data as a list. The row_list
variable is updated every time the table updates.
Recommendations
- Use
use_row_list
for listening to table updates: If you need to listen to a table for one row of data as a list, useuse_row_list
. - Use table operations to filter to one row: If your table has multiple rows and columns, use table operations such as
.where
,.select
and.reverse
to filter to the row you want to listen to.use_row_list
always uses the first row of the table. - Pass a Sentinel value to
use_row_list
: If you want to use a default value when the table is empty, pass a sentinel value touse_row_list
. The default sentinel value isNone
, which is returned when the table is empty.
Empty tables
If the table is empty, the value of row_list
will return the value of None
.
from deephaven import time_table, ui
import datetime as dt
@ui.component
def ui_table_row_list(table):
row_list = ui.use_row_list(table)
if row_list is None:
return ui.heading("No data yet.")
return ui.heading(f"Row list: {row_list}")
start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_row_list = ui_table_row_list(
time_table("PT1s", start_time=start_time).update("x=i").tail(1)
)
You can optionally provide a sentinel
value to return when the table is empty instead.
from deephaven import time_table, ui
import datetime as dt
@ui.component
def ui_table_row_list(table):
row_list = ui.use_row_list(table, sentinel="No data yet.")
return ui.heading(f"Row list: {row_list}")
start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_row_list = ui_table_row_list(
time_table("PT1s", start_time=start_time).update("x=i").tail(1)
)
Null values
If the table has a null
value in the first row, the value for that cell will be pandas.NA
.
from deephaven import time_table, ui
import datetime as dt
import pandas as pd
@ui.component
def ui_table_row_list(table):
row_list = ui.use_row_list(table)
if row_list is None:
return ui.heading("No data yet.")
if pd.isna(row_list[1]):
return ui.heading("x is null value.")
return ui.heading(f"Row list: {row_list}. Value of X is {row_list[1]}")
start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_row_list = ui_table_row_list(
time_table("PT1s", start_time=start_time).update("x=i%2==0?null:i").tail(1)
)
API reference
Return the first row of the table as a list. The table should already be filtered to only have a single row.
Returns: list[Any] | Any | None
The first row of the table as a list or the sentinel value.
Parameters | Type | Default | Description |
---|---|---|---|
table | Table | None | The table to extract the row from. | |
sentinel | Any | None | The sentinel value to return if the table is ticking but empty. Defaults to None. |