Filter Transform

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The filter transform removes objects from a data stream based on a provided filter expression or filter object.

{
  ...
  "transform": [
    {"filter": ...} // Filter Transform
     ...
  ],
  ...
}

Vega-Lite filter transforms must have the filter property describing the predicate for the filtering condition.

Property Type Description
filter LogicalOperand

Required. The filter property must be one of the predicate definitions:

1) an expression string, where datum can be used to refer to the current data object

2) one of the field predicates: equal, lt, lte, gt, gte, range, or oneOf.

3) a selection predicate

4) a logical operand that combines (1), (2), or (3).

Filter Expression

For an expression string, each datum object can be referred using bound variable datum. For example, setting filter to "datum.b2 > 60" would make the output data includes only items that have values in the field b2 over 60.

Field Predicate

For a field predicate, a field must be provided along with one of the predicate properties: equal, lt (less than), lte (less than or equal), gt (greater than), gte(greater than or equal), range, or oneOf. Values of these operators can be primitive types (string, number, boolean) or a DateTime definition object to describe time. In addition, timeUnit can be provided to further transform a temporal field.

Field Equal Predicate

Property Type Description
equal String | Number | Boolean | DateTime

Required. The value that the field should be equal to.

For example, to check if the car_color field’s value is equal to "red", we can use the following filter:

{"filter": {"field": "car_color", "equal": "red"}}

Field Less Than Predicate

Property Type Description
lt String | Number | DateTime

Required. The value that the field should be less than.

For example, to check if the height field’s value is less than 180, we can use the following filter:

{"filter": {"field": "height", "lt": 180}}

Field Less Than or Equals Predicate

Property Type Description
lte String | Number | DateTime

Required. The value that the field should be less than or equals to.

For example, to check if the Year field’s value is less than or equals to "2000", we can use the following filter:

{"filter": {"timeUnit": "year", "field": "Year", "lte": "2000"}}

Field Greater Than Predicate

Property Type Description
gt String | Number | DateTime

Required. The value that the field should be greater than.

To check if the state field’s value is greater than "Arizona" by string comparison, we can use the following filter: (Note: Standard Javascript string comparison is done, ie., “A” < “B”, but “B” < “a”)

{"filter": {"field": "state", "gt": "Arizona"}}

Field Greater Than or Equals Predicate

Property Type Description
gte String | Number | DateTime

Required. The value that the field should be greater than or equals to.

For example, to check if the height field’s value is greater than or equals to 0, we can use the following filter:

{"filter": {"field": "height", "gte": 0}}

Field Range Predicate

Property Type Description
range Number[] | DateTime[] | Null[]

Required. An array of inclusive minimum and maximum values for a field value of a data item to be included in the filtered data.

Examples

  • {"filter": {"field": "x", "range": [0, 5]}} checks if the x field’s value is in range [0,5] (0 ≤ x ≤ 5).
  • {"filter": {"timeUnit": "year", "field": "date", "range": [2006, 2008] }} checks if the date’s value is between year 2006 and 2008.
  • {"filter": {"field": "date", "range": [{"year": 2006, "month": "jan", "date": 1}, {"year": 2008, "month": "feb", "date": 20}] }} checks if the date’s value is between Jan 1, 2006 and Feb 20, 2008.

Field One-Of Predicate

Property Type Description
oneOf String[] | Number[] | Boolean[] | DateTime[]

Required. A set of values that the field’s value should be a member of, for a data item included in the filtered data.

For example, {"filter": {"field": "car_color", "oneOf": ["red", "yellow"]}} checks if the car_color field’s value is "red" or "yellow".

Field Valid Predicate

Property Type Description
valid Boolean

Required. If set to true the field’s value has to be valid, meaning both not null and not NaN.

For example, {"filter": {"field": "car_color", "valid": true}} checks if the car_color field’s value is valid meaning it is both not null and not NaN.

Selection Predicate

For a selection predicate, a selection name must be provided.

Property Type Description
selection String | Object

Required. Filter using a selection name.

For example, with {"filter": {"selection": "brush"}}, only data values that fall within the selection named brush will remain in the dataset as shown below.

All selection composition can be used here as well. For instance, {"filter": {"selection": {"and": ["alex", "morgan"]}}} filters for data values that are within both the alex and morgan selections.