Groovy - List unique(boolean mutate, Comparator comparator) method

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Description

Groovy List unique(boolean mutate, Comparator comparator) method modifies the list by removing any duplicates. If mutate is true, then original list is modified as well. Duplicates are removed using Groovy's default number-aware comparator. Comparator is used to determine unique items.

Syntax

public List unique(boolean mutate, Comparator comparator)

Parameters

• mutate − if true, then original list is modified as well.

• comparator − a comparator to check uniqueness of elements.

Return Value

A list of unique elements of the list.

Example - Getting Unique elements from a List of Integers

Following is an example of the usage of this method −

main.groovy

import org.codehaus.groovy.runtime.NumberAwareComparator

def lst = [11, 12, 13, 10, 15, 11, 10, 12, 15]

// getting list of unique elements 
uniqueList = lst.unique(false, new NumberAwareComparator())
println(uniqueList)

Output

When we run the above program, we will get the following result −

[11, 12, 13, 10, 15]

Example - Getting Unique elements from a List of Strings

Following is an example of the usage of this method −

main.groovy

import org.codehaus.groovy.runtime.NumberAwareComparator

def lst = ["Apple","Mango","Orange","Papaya","Apple", "Apple"]

// getting list of unique elements 
uniqueList = lst.unique(false, new NumberAwareComparator())
println(uniqueList)

Output

When we run the above program, we will get the following result −

[Apple, Mango, Orange, Papaya]

Example - Getting Unique elements from a List of Objects

Following is an example of the usage of this method −

main.groovy

def lst = [new Student(1, "Julie"),new Student(2, "Robert"),new Student(1, "Julie")]

// getting list of unique and even elements 
uniqueList = lst.unique(false, new RollNoComparator())
println(uniqueList)

class RollNoComparator implements Comparator {
    public int compare(Object obj1, Object obj2){
        return ((Student)obj1).getRollNo() - ((Student)obj2).getRollNo()
    }
}

class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public boolean equals(Object obj) {
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
   
   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

Output

When we run the above program, we will get the following result −

[[ 1, Julie ], [ 2, Robert ]]