Transform Aggregate

An aggregate transformation offers aggregating one or more fields. Because aggregate drops columns that are not specified by aggregate or groupby, make sure that include all fields needed to be aggregated.

Aggregate properties

Property Type Description
aggregate Array[Object] One or more data aggregation operation.
groupby Array[String] Nominal fields to group the aggregates by.

aggregate operation definition

Property Type Description
op String An aggregate operation.
field String|Array[String] A field(s) to aggregate. Some operations require two fields.
p Number[0-1] A quantile threshould.
as String (Optional) A new field name.

Supported aggregate operations

For detailed documentation, refer to this page (Arquero).

Zero-field operation

No field property is required. If provided, it will be ignored.

  • count: the count of elements

Single-field operation

The field should be a string for a single field.

  • valid: the number of valid items in a variable

  • distinct: the number of distinct items in a variable

  • mean/average: the mean of a variable
  • mode: the mode of a variable
  • median: the median of a variable
  • quantile: the p quantile value of a variable
  • stdev: the standard deviation of a variable
  • stdevp: the population standard deviation of a variable
  • variance: the variance of a variable

  • variancep: the population variance of a variable

  • sum: the sum of a variable
  • product: the product (multiplication) of a variable
  • max: the maximum value of a variable
  • min: the min value of a variable

Double-field operation

The field should be a string for a single field.

  • corr: the correlation of two variables
  • covariance: the covariance of two variables
  • covariancep: the population covariance of two variables

Usage pattern

JSON

{
  ...
  "transform" : [
    {
      "aggregate": [
        { "op": "count", "as": "count" },
        { "op": "mean", "field": "cost", "as": "mean_cost" },
        { "op": "quantile", "field": "cost", "p": 0.7 "as": "top_30_cost" },
        { "op": "covariance", "field": ["cost", "expense"], "as": "cost_expense_covariance" }
      ],
      "groupby": [
        "category", "country"
      ]
    },
  ]
  ...
}

JavaScript

let stream = new Erie.Stream();
...
let aggregate = new Erie.Aggregate();
aggregate.add("count", "count"); // op, as
aggregate.add("mean", "cost", "count");
aggregate.add("quantile", "cost", "top_30_cost", 0.7); // op, field, as, p
aggregate.add("covariance", ["cost", "expense"], "cost_expense_covariance");
aggregate.groupby(["category", "country"]);
stream.transform.add(aggregate);
...
© Hyeok Kim