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 is None:
        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, use use_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 to use_row_list. The default sentinel value is None, 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.