Operator Type:
Operator Scope of Action:
Operator Purpose:
Operator First Added:
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Function [other Function type actions]
Conditional Group [operators of similar scope]
Set & List creation [other Set & List creation operators]
Baseline
A function collect_if() builds a List; see collect() for a related new operator.
collect_if(group,condition,attribute)
builds a set by collecting all the notes corresponding to group, testing each note to see if it meets condition, and adding the value of the designated attribute to the set.
group may be any of {children,descendants,siblings,ancestors,all}. In addition, group may be argument that designates a particular (single) note other than this.
condition is a valid conditional test - i.e. it equates to true when matched.
attribute can be any expression, but is typically an attribute.
For example,
collect_if(children,$Status=="Important",$Name)
will construct a set of the names of all of this note's important children.
Note that collect_if's function is related to agents; many tasks you might perform with collect_if could be done as well, or better, with an agent.
If a list of unique values is required - i.e. a set rather than a list, simply pass the output to a Set attribute. Thus if:
$MyList = collect_if(children,$Age>6,$FavFruit) $MyList is "Apples;Oranges;Pears;Apples"
$MySet = collect(children,$Age>6,$FavFruit) MySet is "Apples;Oranges;Pears;"