Selecting a Subset of Keys

To select a subset of key-value pairs from an object (perhaps with many key-value pairs), we can use the built-in project() function:

let $crew := {
  "Captain" : "Kirk",
  "First Officer" : "Spock",
  "Engineer" : "Scott",
  "Doctor" : "McCoy",
  "Communications Officer" : "Uhura"
}
return project( $crew, ( "Captain", "First Officer" ) )

{
  "Captain" : "Kirk",
  "First Officer" : "Spock"
}

The project() function takes a sqequence of objects to select from and a sequence of keys to select from every object.