Combines an iterable of values in a keyed collection of elements.
See more information in the Beam Programming Guide.
In the following examples, we create a pipeline with a
PCollection of produce.
Then, we apply
CombineValues in multiple ways to combine the keyed values in the
CombineValues accepts a function that takes an
iterable of elements as an input, and combines them to return a single element.
CombineValues expects a keyed
PCollection of elements, where the value is an iterable of elements to be combined.
Example 1: Combining with a predefined function
We use the function
which takes an
iterable of numbers and adds them together.
Example 2: Combining with a function
We want the sum to be bounded up to a maximum value, so we use saturated arithmetic.
We define a function
saturated_sum which takes an
iterable of numbers and adds them together, up to a predefined maximum number.
Example 3: Combining with a lambda function
We can also use lambda functions to simplify Example 2.
Example 4: Combining with multiple arguments
You can pass functions with multiple arguments to
They are passed as additional positional arguments or keyword arguments to the function.
In this example, the lambda function takes
max_value as arguments.
Example 5: Combining with a
The more general way to combine elements, and the most flexible, is with a class that inherits from
CombineFn.create_accumulator(): This creates an empty accumulator. For example, an empty accumulator for a sum would be
0, while an empty accumulator for a product (multiplication) would be
CombineFn.add_input(): Called once per element. Takes an accumulator and an input element, combines them and returns the updated accumulator.
CombineFn.merge_accumulators(): Multiple accumulators could be processed in parallel, so this function helps merging them into a single accumulator.
CombineFn.extract_output(): It allows to do additional calculations before extracting a result.
You can use the following combiner transforms:
Last updated on 2023/11/27
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