Filter

The "filter" transform removes data objects based on a predicate expression or a selection predicate.

Parameters

Predicate Expression

expr Required

Type: string

An expression string. The data object is removed if the expression evaluates to false.

Selection Predicate

empty

Type: boolean

If true, the filter retains all data objects when the selection is empty.

Default: true

fields

Type: object

An optional mapping of positional channels to fields. Used to determine which fields are checked against the selection intervals.

param Required

Type: string

A selection parameter. The data object is removed if it is not part of the selection.

Example

Filtering by a Predicate Expression

{
  "type": "filter",
  "expr": "datum.p <= 0.05"
}

The example above passes through all rows for which the field p is less than or equal to 0.05.

Filtering by a Selection Predicate

Interval selections in GenomeSpy are defined by their data extent along the x and/or y channels. When filtering data based on a selection, you must explicitly map the visual channels (x or y) to the corresponding data fields to ensure correct filtering. This ensures that the filter correctly interprets the selection in the context of your dataset.

{
  "data": { "url": "sincos.csv" },

  "params": [{ "name": "brush" }],

  "vconcat": [
    {
      "height": 30,
      "transform": [
        { "type": "collect" },
        {
          "type": "filter",
          "param": "brush",
          "fields": { "x": "x", "y": "sin" }
        },
        { "type": "aggregate" },
        {
          "type": "formula",
          "as": "text",
          "expr": "datum.count + ' points selected'"
        }
      ],
      "mark": { "type": "text", "size": 20 },
      "encoding": {
        "text": { "field": "text" }
      }
    },
    {
      "params": [
        {
          "name": "brush",
          "value": { "x": [2.5, 4], "y": [-0.6, 0.6] },
          "select": {
            "type": "interval",
            "encodings": ["x", "y"]
          },
          "push": "outer"
        }
      ],

      "mark": { "type": "point", "size": 100 },

      "encoding": {
        "x": { "field": "x", "type": "quantitative" },
        "y": { "field": "sin", "type": "quantitative" }
      }
    }
  ]
}