Beam / Dataflow 2.2.0-从pcollection中提取前n个元素

Question

Is there any way to extract first n elements in a beam pcollection? The documentation doesn't seem to indicate any such function. I think such an operation would require first a global element number assignment and then a filter - would be nice to have this functionality.

I use Google DataFlow Java SDK 2.2.0 .

Answer 1

PCollection's are unordered per se, so the notion of "first N elements" does not exist - however:

• In case you need the top N elements by some criterion, you can use the Top transform .

• In case you need any N elements, you can use Sample .