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Version: Python

forward_fill

forward_fill creates a forward-fill null replacement operator to be used in an update_by table operation. This operation is forward-only.

Syntax​

forward_fill(cols: list[str]) -> UpdateByOperation

Parameters​

ParameterTypeDescription
colslist[str]

The column(s) to be operated on. These can include expressions to rename the output columns (e.g., NewCol = Col). If None, a forward fill is performed on all applicable columns in the table.

Returns​

An UpdateByOperation to be used in an update_by table operation.

Examples​

Forward fill all columns of a table​

The following example performs a forward_fill to replace null values with the most recent non-null. No columns are given to the UpdateByOperation, so the operation is applied to all non-grouping columns in the source table. Also, no grouping columns are given, so the operation is applied to all rows.

from deephaven.updateby import forward_fill
from deephaven.constants import NULL_INT
from deephaven import empty_table

source = empty_table(10).update(
    [
        "Letter = (i % 2 == 0) ? `A` : `B`",
        "X = (i % 3 == 0) ? NULL_INT : i",
        "Y = (i % 3 == 1) ? i : NULL_INT",
    ]
)

result = source.update_by(ops=forward_fill(cols=[]))

Forward fill all non-key columns​

The following example builds on the previous by specifying Letter as the grouping column. Thus, the forward fill is applied to all columns except for Letter, and is done on a per-letter basis.

from deephaven.updateby import forward_fill
from deephaven.constants import NULL_INT
from deephaven import empty_table

source = empty_table(10).update(
    [
        "Letter = (i % 2 == 0) ? `A` : `B`",
        "X = (i % 3 == 0) ? NULL_INT : i",
        "Y = (i % 3 == 1) ? i : NULL_INT",
    ]
)

result = source.update_by(ops=forward_fill(cols=[]), by=["Letter"])

Forward fill one column grouped by multiple key columns​

The following example builds on the previous by specifying Letter and Truth as the grouping columns. Thus, groups are defined by unique combinations of letter and boolean, respectively. The forward_fill is only applied to the X column, so the Y column has no operations applied to it.

from deephaven.updateby import forward_fill
from deephaven.constants import NULL_INT
from deephaven import empty_table

source = empty_table(10).update(
    [
        "Letter = (i % 2 == 0) ? `A` : `B`",
        "Truth = randomBool()",
        "X = (i % 3 == 0) ? NULL_INT : i",
        "Y = (i % 3 == 1) ? i : NULL_INT",
    ]
)

result = source.update_by(ops=forward_fill(cols=["X"]), by=["Letter", "Truth"])