Sort a list of Employee records by salary.

← Operators and Expressions · Ref: Q1085

Sort records by one field with a comparator function given to sort:

  bySalary() as pure
    ->
      left as Employee
      right as Employee
    <- rtn as Integer: left.salary <=> right.salary

  sorted <- cat staff | sort by bySalary | collect as List of Employee

A plain '| sort' uses the type's own <=>, and 'default operator' generates <=> across all fields in declaration order (name first here). A different ordering for one use is a comparator function given to 'sort by', never a second <=>.

See Q1073 for descending sort. See Q1082 for basic comparison.

Example

defines module qa.operators.sortrecordsbyfield

  defines record

    Employee
      name as String: String()
      salary as Float: 0.0

      Employee()
        ->
          name as String
          salary as Float
        this.name :=: name
        this.salary :=: salary

      default operator

  defines function

    bySalary() as pure
      ->
        left as Employee
        right as Employee
      <- rtn as Integer: left.salary <=> right.salary

  defines program

    SortRecordsByFieldDemo()
      stdout <- Stdout()

      staff <- List() of Employee
      staff += Employee("Alice", 75000.0)
      staff += Employee("Bob", 55000.0)
      staff += Employee("Charlie", 92000.0)
      staff += Employee("Diana", 68000.0)

      stdout.println("Unsorted:")
      cat staff > stdout

      //Sort by one field: a comparator function given to sort
      sorted <- cat staff | sort by bySalary | collect as List of Employee
      stdout.println("Sorted:")
      cat sorted > stdout

Common mistakes

E50060 — EK9 List has no .sort() method; sort via a stream pipeline 'cat list | sort by comparator | collect as List of T'. See ek9 -h E50060 for details.

Incorrect:

sorted <- staff.sort()

Correct:

sorted <- cat staff | sort by bySalary | collect as List of Employee

Other ways to ask this

Order objects in a list using a stream sort pipeline
Arrange records from lowest to highest value
In Java I'd use Collections.sort with Comparator.comparing(). How in EK9?
I have a list of employees and need to sort them by pay

Coming from another language?

Java: Collections.sort(list, Comparator.comparing(Employee::getSalary)). Python: sorted(employees, key=lambda e: e.salary). Rust: sort_by_key(). EK9: cat list | sort by comparator | collect as List of T.

Keywords: ascending, pipeline, order, stream, record, list, sort