Aggregate¶

The "aggregate" transform summarizes data fields using aggregate functions, such as "sum" or "max". The data can be grouped by one or more fields, which results in a list of objects with the grouped fields and the aggregate values.

Parameters¶

as: Type: array
The names for the output fields corresponding to each aggregated field. If not provided, names will be automatically created using the operation and field names (e.g., sum_field, average_field).
fields: Type: array
The data fields to apply aggregate functions to. This array should correspond with the ops and as arrays. If no fields or operations are specified, a count aggregation will be applied by default.
groupby: Type: array
The fields by which to group the data. If these are not defined, all data objects will be grouped into a single category.
ops: Type: array
The aggregation operations to be performed on the fields, such as "sum", "average", or "count".

Available aggregate functions¶

Aggregate functions are applied to the data fields in each group.

"count": Count the number of records in each group.
"valid": Count the number of non-null and non-NaN values.
"sum": Sum the values.
"mean": Calculate the mean value.
"average": A synonym for "mean".
"median": Calculate the median value.
"min": Find the minimum value.
"max": Find the maximum value.
"variance": Calculate the variance.

Example¶

Given the following data:

x	y
first	123
first	456
second	789

... and configuration:

{
  "type": "aggregate",
  "groupby": ["x"]
}

A new list of data objects is created:

x	count
first	2
second	1

Calculating min and max¶

{
  "data": {
    "values": [
      { "Category": "A", "Value": 5 },
      { "Category": "A", "Value": 9 },
      { "Category": "A", "Value": 9.5 },
      { "Category": "B", "Value": 3 },
      { "Category": "B", "Value": 5 },
      { "Category": "B", "Value": 7.5 },
      { "Category": "B", "Value": 8 }
    ]
  },

  "encoding": {
    "y": { "field": "Category", "type": "nominal" }
  },

  "layer": [
    {
      "encoding": {
        "x": { "field": "Value", "type": "quantitative" }
      },
      "mark": "point"
    },
    {
      "transform": [
        {
          "type": "aggregate",
          "groupby": ["Category"],
          "fields": ["Value", "Value"],
          "ops": ["min", "max"],
          "as": ["minValue", "maxValue"]
        }
      ],
      "encoding": {
        "x": { "field": "minValue", "type": "quantitative" },
        "x2": { "field": "maxValue" }
      },
      "mark": "rule"
    }
  ]
}