group and cogroup

Adds one or more columns to a group. If data is grouped by a value that’s null in a row, that whole row is removed from the result.

Syntax:

or

Group by 1 dimension:

a = group a by year;

This example is a simple cogroup operation on 2 datasets:

You can cogroup more than 2 datasets:

This example performs a cogroup operation:

You can’t have the same stream on both sides of a cogroup operation. To perform a cogroup operation on 1 dataset, load the dataset twice so you have 2 streams. You can also load 1 dataset and filter it into 2 different streams:

This code throws an error because it performs a cogroup operation on a single stream, a:

To use aggregate functions when cogrouping, specify which input side to use in the aggregate function. For example, if you have an a side and a b side, and each contains a particular measure, use one of these syntaxes:

This query is valid because it uses the third syntax form to specify that miles comes from the a side.

This query isn’t valid because miles doesn't specify which side it is coming from:

If a lens or dashboard has a cogroup query, specify the input stream for projections and for count() aggregations on cogroup queries, as in this example:

Outer cogrouping combines groups as an outer join. For the half-matches, null rows are added. The grouping keys are taken from the input that provides the value.

Syntax:

Specify left, right, or full to indicate whether to perform a left outer join, a right outer join, or a full join.

Example: z = cogroup x by (day,origin) left, y by (day,airport);

You can apply an outer cogrouping across more than 2 sets of data. This example does a left outer join from a to b, with a right join to c:

result = cogroup a by keya left, b by keyb right, c by keyc;