AccumulateBy
Groups records and reduces each group to a single record per group.
public <I extends java.io.Serializable> GearsBuilder<I> accumulateBy(
gears.operations.ExtractorOperation<T> extractor,
gears.operations.AccumulateByOperation<T,I> accumulator)
public <I extends java.io.Serializable> GearsBuilder<I> accumulateBy(
gears.operations.ValueInitializerOperation<I> valueInitializer,
gears.operations.ExtractorOperation<T> extractor,
gears.operations.AccumulateByOperation<T,I> accumulator)
Iterates through the records in the pipe, groups them based on the provided extractor, and then reduces each group to a single record per group with the accumulator function.
The initial value of the accumulator is null unless you provide a value initializer operation as a parameter.
Parameters
Type parameters:
| Name | Description |
|---|---|
| I | The template type of the returned builder |
Function parameters:
| Name | Type | Description |
|---|---|---|
| accumulator | A function with logic to update the accumulator value with each record | |
| extractor | ExtractorOperation |
Extracts a specific value from each record |
| valueInitializer | ValueInitializerOperation | Whenever the accumulated value is null, use this function to initialize it |
Returns
Returns a GearsBuilder object with a new template type.
Examples
Both of the following examples count the number of unique values.
Without the valueInitializer parameter:
GearsBuilder.CreateGearsBuilder(reader).
accumulateBy(r->{
return r.getStringVal();
},(k, a, r)->{
Integer ret = null;
if(a == null) {
ret = 0;
}else {
ret = (Integer)a;
}
return ret + 1;
});
With the valueInitializer parameter:
GearsBuilder.CreateGearsBuilder(reader).
accumulateBy(()->{
return 0;
},r->{
return r.getStringVal();
},(k, a, r)->{
return a + 1;
});