use_row_data

use_row_data lets you use the data of the first row of a table as a dictionary. 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(table):
    row_data = ui.use_row_data(table)
    if row_data is None:
        return ui.heading("No data yet.")
    return ui.heading(f"Row data is {row_data}. Value of X is {row_data['x']}")


table_row = ui_table_row(time_table("PT1s").update("x=i").reverse())

In the above example, ui_table_row is a component that listens to a table and displays the first row of data. The row_data variable is updated every time the table updates.

Recommendations

Use use_row_data for listening to table updates: If you need to listen to a table for one row of data, use use_row_data.
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_data always uses the first row of the table.
Pass a Sentinel value to use_row_data: If you want to use a default value when the table is empty, pass a sentinel value to use_row_data. 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_data will return the value of None.

from deephaven import time_table, ui
import datetime as dt


@ui.component
def ui_table_row(table):
    row_data = ui.use_row_data(table)
    if row_data is None:
        return ui.heading("No data yet.")
    return ui.heading(f"Row data: {row_data}.")


start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_row = ui_table_row(
    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(table):
    row_data = ui.use_row_data(table, sentinel={"x": "No data yet."})
    return ui.heading(f"Row data: {row_data}. Value of 'x' is {row_data['x']}")


start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_row = ui_table_row(
    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(table):
    row_data = ui.use_row_data(table)
    if row_data is None:
        return ui.heading("No data yet.")
    if pd.isna(row_data["x"]):
        return ui.heading("Value of 'x' is null.")
    return ui.heading(f"Row data: {row_data}. Value of 'x' is {row_data['x']}")


start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_row = ui_table_row(
    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 dictionary. The table should already be filtered to only have a single row.

Returns: Dict[str, Any] | Any | None The first row of the table as a dictionary 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.