Selects a subset of columns from an input dataset and forwards it for further processing.
Column selection is usually a pre-step for aggregation.
The column selection processor operates on any kind of input dataset.
The processor returns the selected columns with the same number of entries (lines).
In the following example we're using an accommodation input dataset. The goal is to output the average accommodation price in each city.
We group by the location and use the average as an aggregation function to get the following result.