reject() Function

Function

reject( predicate, list, context )

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

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 and alternatives

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

Examples

Rejecting items in a list

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

Rejecting items in a list with context

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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.

Learn more about a!isUserMemberOfGroup().

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.

Learn more about a!isUserMemberOfGroup().

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.

Learn more about a!isUserMemberOfGroup().

Rejecting items in 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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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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