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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 PCollection.

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 sum 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 CombineValues. They are passed as additional positional arguments or keyword arguments to the function.

In this example, the lambda function takes values and max_value as arguments.

Example 5: Combining with a CombineFn

The more general way to combine elements, and the most flexible, is with a class that inherits from CombineFn.

You can use the following combiner transforms:

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