reject() Function

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

Parameters

reject( predicate, list, context )

Returns

Any Type Array

Using the function

The following sections cover important details about the reject() function.

Using the predicate parameter

In the predicate parameter of reject(), enter fn!functionName or a!functionName to reference an expression function, or 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).

Unsupported functions

The reject() function doesn't support a!forEach() in rules that you use as the predicate.

Examples

The following examples demonstrate the reject() function.

To experiment with examples, copy and paste the expression into an expression rule and click TEST RULE to see the output.

Rejecting items in a list

This example rejects null and empty values from a list using a!isNullOrEmpty as the predicate.

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reject(
  a!isNullOrEmpty,
  {1, 2, null, 3, null, 4}
)

Returns {1, 2, 3, 4}.

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

Rejecting items in a list with context

This example uses the context parameter to pass fixed values into each evaluation of the predicate.

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

Returns {"user2"} when user1 and user3 are members of the group referenced by cons!csaAdmins. a!isUserMemberOfGroup has 3 parameters: username, groups, and matchAllGroups. The reject() list corresponds to username, and the list of values provided in the context parameter are used as the next two parameters, groups & matchAllGroups.

Rejecting items in a list with context for more than 2 parameters

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

Returns {"user2", "user3"} when only user1 is a member of all the groups referenced in cons!allGroups. a!isUserMemberOfGroup has 3 parameters: username, groups, and matchAllGroups. The reject() list corresponds to username, and the list of values provided in the context parameter are used as the next two parameters, groups & matchAllGroups.

Rejecting items in a list with context for more than 2 parameters which accept lists

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

Returns {"user2", "user3"}. In this case, 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.

Rejecting items in a list with a custom expression rule

This example rejects dates that are later than a reference date. It uses 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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reject(
  rule!isDateLater,
  {date(1950, 2, 3), date(1950, 6, 23), date(1950, 5, 2)},
  date(1950, 4, 7)
)

Returns {2/3/1950}

Feature compatibility

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