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

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:

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

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