Aggregate Transform

The aggregate transform groups and summarizes an input data stream to produce a derived output stream. Aggregate transforms can be used to compute counts, sums, averages and other descriptive statistics over groups of data objects.

Transform Parameters

Property Type Description
groupby Field[ ] The data fields to group by. If not specified, a single group containing all data objects will be used.
fields Field[ ] The data fields for which to compute aggregate functions. This array should align with the ops and as arrays. If no fields and ops are specified, a count aggregation will be used by default.
ops String[ ] The aggregation operations to apply to the fields, such as sum, average or count. See the aggregate operation reference for more.
as String[ ] The output field names to use for each aggregated field in fields. If not specified, names will be automatically generated based on the operation and field names (e.g., sum_field, average_field).
cross Boolean Indicates if the full cross-product of all groupby values should be included in the aggregate output (default false). If set to true, all possible combinations of groupby field values will be considered and zero count groups will be generated and returned for combinations that do not occur in the data itself. Cross-product output act as if the drop parameter is false. In the case of streaming updates, the number of output groups will increase if new groupby field values are observed; all prior groups will be retained. This parameter can be useful for generating facets that include groups for all possible partitions of the data.
drop Boolean Indicates if empty (zero count) groups should be dropped (default true). When a data stream updates (for example, in response to interactive filtering), aggregation groups may become empty. By default, the group is removed from the output. However, in some cases (such as histograms), one may wish to retain empty groups.

Aggregate Operation Reference

All valid aggregate operations.

Operation Description
count The total count of data objects in the group.
valid The count of field values that are not null, undefined or NaN.
missing The count of null or undefined field values.
distinct The count of distinct field values.
sum The sum of field values.
mean The mean (average) field value.
average The mean (average) field value. Identical to mean.
variance The sample variance of field values.
variancep The population variance of field values.
stdev The sample standard deviation of field values.
stdevp The population standard deviation of field values.
stderr The standard error of field values.
median The median field value.
q1 The lower quartile boundary of field values.
q3 The upper quartile boundary of field values.
ci0 The lower boundary of the bootstrapped 95% confidence interval of the mean field value.
ci1 The upper boundary of the bootstrapped 95% confidence interval of the mean field value.
min The minimum field value.
max The maximum field value.
argmin An input data object containing the minimum field value.
argmax An input data object containing the maximum field value.


For the following input data:

  {"foo": 1, "bar": 1},
  {"foo": 1, "bar": 2},
  {"foo": null, "bar": 3}

The aggregate transform

  "type": "aggregate",
  "fields": ["foo", "bar", "bar"],
  "ops": ["valid", "sum", "median"],
  "as": ["v", "s", "m"]

produces the output:

[{"v": 2, "s": 6, "m": 2}]