FunctionCopy link to clipboard
filter( predicate, list, context )
Calls a predicate for each item in a list and returns any items for which the returned value is true.
ParametersCopy link to clipboard
| Keyword | Type | Description |
|---|---|---|
|
|
Function, Rule, or Data Type Constructor |
Expression that returns a Boolean (true or false). |
|
|
Any Type Array |
List of elements that the predicate iterates through. |
|
|
Any Type Array |
Variable number of parameters passed directly into each predicate evaluation. |
ReturnsCopy link to clipboard
Any Type Array
Usage considerationsCopy link to clipboard
Referencing expressions and rulesCopy link to clipboard
Use fn!functionName or a!functionName to reference an expression function and rule!ruleName to reference a rule.
Using rules or functions with multiple argumentsCopy link to clipboard
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).
LimitationsCopy link to clipboard
a!forEach() cannot be used within rules used in this function.
ExamplesCopy link to clipboard
Filtering a listCopy link to clipboard
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filter(
a!isNotNullOrEmpty,
{1, 2, null, 3, null, 4}
)
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Returns {1, 2, 3, 4}.
Filtering with contextCopy link to clipboard
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 contextCopy link to clipboard
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filter(
a!isUserMemberOfGroup,
{"user1", "user2", "user3"},
cons!csaAdmins
)
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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 parametersCopy link to clipboard
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filter(
a!isUserMemberOfGroup,
{"user1", "user2", "user3"},
{cons!allGroups, true}
)
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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 listsCopy link to clipboard
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filter(
a!isUserMemberOfGroup,
{"user1", "user2", "user3"},
merge({cons!csaAdmins, cons!csaProfs}, {true, true})
)
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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 ruleCopy link to clipboard
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
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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)
)
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Returns {6/23/1950, 5/2/1950}
Feature compatibilityCopy link to clipboard
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. |
| Process Autoscaling | Compatible |