use_cell_data

use_cell_data lets you use the cell data of the first cell (first row in the first column) in a table. 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_first_cell(table):
    cell_value = ui.use_cell_data(table)
    return ui.heading(f"The first cell value is {cell_value}")


table_first_cell = ui_table_first_cell(time_table("PT1s").tail(1))

In the above example, ui_table_first_cell is a component that listens to the last row of a table and displays the value of the first cell. The cell_value variable is updated every time the table updates.

Recommendations

Use use_cell_data for listening to table updates: If you need to listen to a table for one cell of data, use use_cell_data.
Use table operations to filter to one cell: Because use_cell_data always uses the top-left cell of the table, you can filter your table to determine what cell to listen to. If your table has multiple rows and columns, use table operations such as .where, .select and .reverse to filter to the desired cell.

Empty tables

If the table is empty, the value of cell_value will return the value of None.

from deephaven import time_table, ui
import datetime as dt


@ui.component
def ui_table_first_cell(table):
    cell_value = ui.use_cell_data(table)
    if cell_value is None:
        return ui.heading("No data yet.")
    return ui.heading(f"The first cell value is {cell_value}")


start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_first_cell = ui_table_first_cell(
    time_table("PT1s", start_time=start_time).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_first_cell(table):
    cell_value = ui.use_cell_data(table, sentinel="No data yet.")
    return ui.heading(f"Cell value: {cell_value}")


start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_first_cell = ui_table_first_cell(
    time_table("PT1s", start_time=start_time).tail(1)
)

Null values

If the table cell is a null value, the value of cell_value will be pandas.NA. You can check for null values using the pandas.isna function.

from deephaven import time_table, ui
import datetime as dt
import pandas as pd


@ui.component
def ui_table_first_cell(table):
    cell_value = ui.use_cell_data(table)
    if cell_value is None:
        return ui.heading("No data yet.")
    if pd.isna(cell_value):
        return ui.heading("Cell value is null.")
    return ui.heading(f"Cell value: {cell_value}")


start_time = dt.datetime.now() + dt.timedelta(seconds=2)
table_first_cell = ui_table_first_cell(
    time_table("PT1s", start_time=start_time)
    .update("x=i%2==0?null:i")
    .select("x")
    .tail(1)
)

Return the first cell of the table. The table should already be filtered to only have a single cell.

Returns: Any The first cell of the table.

Parameters	Type	Default	Description
table	Table \| None		The table to extract the cell from.
sentinel	Any	None	The sentinel value to return if the table is ticking but empty. Defaults to None.