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filter() Function

Function

filter( predicate, list, context )

Calls a predicate for each item in a list and returns any items for which the returned value is true.

Parameters

Keyword Type Description

predicate

Function, Rule, or Data Type Constructor

Expression that returns a Boolean (true or false).

list

Any Type Array

List of elements that the predicate iterates through.

context

Any Type Array

Variable number of parameters passed directly into each predicate evaluation.

Returns

Any Type Array

Usage considerations

Referencing expressions and rules

Use fn!functionName or a!functionName to reference an expression function and rule!ruleName to reference a rule.

Using rules or functions with multiple arguments

To use rules or functions that take more than two arguments, use the merge() function. For example, given a rule g(x, y, z), reduce(rule!g, i, merge({a, b, c}, {d, e, f})) returns g(g(g(i, a, d), b, e), c, f).

Limitations

a!forEach() cannot be used within rules used in this function.

Examples

Filtering a list

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filter(
  a!isNotNullOrEmpty,
  {1, 2, null, 3, null, 4}
)

Returns {1, 2, 3, 4}.

Filtering with context

To help demonstrate how the context parameter works in looping expressions, let's look at an example.

Imagine you're building an expression that uses looping to analyze group membership in your application. You have four Group constants configured in the following ways:

Constant Group(s) referenced Group membership
cons!csaAdmins CSA Administrators user1, user3
cons!csaProfs CSA Professors user1, user2, user4, user5, user6, user7
cons!csaBuilding1 CSA Building 1 user1, user2, user3, user5, user6, user7
cons!allGroups CSA Adminstrators, CSA Professors, CSA Building 1 See above

The following SAIL expressions reference these constants to show how context works when checking items in a list.

Note:  You'll need to adapt these expression examples for your own purposes, since the examples reference constants that may not exist in your Appian environment.

Filtering a list with context

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filter(
  a!isUserMemberOfGroup,
  {"user1", "user2", "user3"},
  cons!csaAdmins
)

Returns {"user1", "user3"}. Since user1 and user3 are members of the group referenced by cons!csaAdmins they will be returned by the function.

Learn more about a!isUserMemberOfGroup().

Filtering a list with context for more than 2 parameters

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filter(
  a!isUserMemberOfGroup,
  {"user1", "user2", "user3"},
  {cons!allGroups, true}
)

Returns {"user1"} when only user1 is a member of all the groups referenced in cons!allGroups. a!isUserMemberOfGroup has 3 parameters: username, groups, and matchAllGroups. The filter() list corresponds to username, and the list of values provided in the context parameter are used as the next two parameters, groups & matchAllGroups.

Learn more about a!isUserMemberOfGroup().

Filtering a list with context for more than 2 parameters which accept lists

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filter(
  a!isUserMemberOfGroup,
  {"user1", "user2", "user3"},
  merge({cons!csaAdmins, cons!csaProfs}, {true, true})
)

Returns {"user1"} when only user1 is a member of the groups referenced in cons!csaAdmins and cons!csaProfs. The merge() function maps the list values to the correct parameters in this example.

Learn more about a!isUserMemberOfGroup().

Filtering a list with a custom expression rule

In this example, we will use a helper rule, rule!isDateLater(value, referenceDate), which is defined as:

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ri!value > ri!referenceDate

Example filter:

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filter(
  rule!isDateLater,
  {date(1950, 2, 3), date(1950, 6, 23), date(1950, 5, 2)},
  date(1950, 4, 7)
)

Returns {6/23/1950, 5/2/1950}

Feature compatibility

The table below lists this function's compatibility with various features in Appian.
Feature Compatibility Note
Portals Compatible
Offline Mobile Compatible
Sync-Time Custom Record Fields Compatible

Can be used to create a custom record field that only evaluates at sync time.

Real-Time Custom Record Fields Incompatible

Custom record fields that evaluate in real time must be configured using one or more Custom Field functions.

Process Reports Incompatible

Cannot be used to configure a process report.

Process Events Incompatible

Cannot be used to configure a process event node, such as a start event or timer event.

Open in Github Built: Thu, Jun 13, 2024 (05:03:21 PM)

filter() Function

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