Predicate

A predicate is used to define an inclusion or exclusion criterion. Predicates are passed to the findElements function, which takes an array of predicate objects as its parameter. A predicate can be defined for a visual property or a data attribute.

Point predicates#

A point predicate matches a single value. This is the default predicate type, so the type field can be omitted.

• {property: _property_, value: _value_} matches a visual property exactly, for example, the following code will return all the text elements in the scene:

    msc.findElements(scene, [{property: "type", value: "text"}])

• {attribute: _attribute_, value: _value_} matches a data attribute exactly, for example, the following code will return all the circles whose data value for Continent is "Asia":

    msc.findElements(scene, [
        {attribute: "Continent", value: "Asia"},
        {property: "type", value: "circle"}
    ])

List predicates#

A list predicate matches any value in a list.

• {type: "list", property: _property_, value: _[values]_} matches any one of the listed property values, for example:

    msc.findElements(scene, [
        {type: "list", property: "type", value: ["text", "rect"]}
    ])

• {type: "list", attribute: _attribute_, value: _[values]_} matches any one of the listed data values, for example:

    msc.findElements(scene, [
        {type: "list", attribute: "event_attribute", value: ["_Start", "_Exit"]}
    ])

Interval predicates#

An interval predicate matches values within a range.

• {type: "interval", property: _property_, value: _[low, high]_} matches elements whose property lies within the specified range, for example:

    msc.findElements(scene, [
        {type: "interval", property: "x", value: [0, 200]}
    ])

• {type: "interval", attribute: _attribute_, value: _[low, high]_} matches elements whose data attribute lies within the specified range, for example:

    msc.findElements(scene, [
        {type: "interval", attribute: "age", value: [20, 50]}
    ])

Combining predicates#

Multiple predicates are combined with logical AND. An element must satisfy all predicates in the array to be returned.

    msc.findElements(scene, [
        {attribute: "name", value: "VMWare"},
        {property: "type", value: "text"}
    ])