Prevent user from selecting duplicate values in custom picker

Question

I have a custom picker field that returns a list of users, 
 I want to be able to prevent the user from selecting the same user more than once. 
 
 Scenario: 
 Users: "John", "James","Sally" 
 
 User comes in and selects "John" as a user on the picker field, then presses "j" the only user that should display is "James". How can I achieve this?

TJ · Answer

May be following code works for you : 
 
 load( a!formLayout( firstColumnContents: { a!pickerFieldCustom( label: "Select User", suggestFunction: rule!TEST_pickerSuggestFn( searchText: _, selectedUsers: ri!selectedUsers ), selectedLabels: ri!selectedUsers, value: ri!selectedUsers, saveInto: ri!selectedUsers ) } ) ) 
 selectedUsers - User (List) 
 
 rule!TEST_pickerSuggestFn 
 with( local!users: { touser( "John" ), touser( "James" ), touser( "Sally" ) }, local!userData: fn!difference( local!users, ri!selectedUsers ), local!matches: where( apply( search( ri!searchText, _ ), local!userData ) ), a!dataSubset( data: index( local!userData, local!matches ), identifiers: index( local!userData, local!matches ) ) ) 
 searchText - Text 
 selectedUsers - User (List)

ankita0004 · Answer

You can use thi code in save into of custom picker 
 
a!save( 
ri!selectedId, 
union(save!value, cast(typeof(save!value), {})) 
)