Multi-threading to the “combine” function

[nilshg]

See

Threading support for DataFrames transforms

If the transformation is thread-safe it would be safe and design is made to ensure this is done the way you want in the future. For GroupedDataFrame we currently use multi-threading already for a sequence of operations. The reason is that usually operations on GroupedDataFrame are more expensive so it was a higher priority to parallelize them. combine under the hood does not differ from transform or select. It is parallelized for GroupedDataFrame but sequential for AbstractDataFrame. Con…