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Version: Python

lazy_update

The lazy_update method creates a new table containing a new cached formula column for each argument.

When using lazy_update, cell values are stored in memory in a cache. Column formulas are computed on-demand and defer computation until it is required. Because it caches the results for the set of input values, the same input values will never be computed twice. Existing columns are referenced without additional memory allocation.

note

The syntax for the lazy_update, update_view, and update methods is identical, as is the resulting table.

lazy_update is recommended for small sets of unique input values. In this case, lazy_update uses less memory than update and requires less computation than update_view. However, if there are many unique input values, update will be more efficient because lazy_update stores the formula inputs and result in a map, whereas update stores the values more compactly in an array.

Syntax​

lazy_update(formulas: Union[str, Sequence[str]]) -> Table

Parameters​

ParameterTypeDescription
formulasUnion[str, Sequence[str]]

Formulas to compute columns in the new table; e.g., "X = A * sqrt(B)".

Returns​

A new table that includes all the original columns from the source table and the newly defined columns.

Examples​

In the following example, a new table is created, containing the square root of column C. Because column C only contains the values 2 and 5, sqrt(2) is computed exactly one time, and sqrt(5) is computed exactly one time. The values are cached for future use.

from deephaven import new_table
from deephaven.column import string_col, int_col

source = new_table(
    [
        string_col("A", ["The", "At", "Is", "On"]),
        int_col("B", [1, 2, 3, 4]),
        int_col("C", [5, 2, 5, 5]),
    ]
)

result = source.lazy_update(formulas=["Y = sqrt(C)"])