Groovy - Map retainAll(Closure closure) method

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Description

Groovy Map retainAll(Closure closure) method retains entries from the Map where entries are satifying the closure and removes other entries.

Syntax

public Object retainAll(Closure closure)

Parameters

closure − a one or two args closure to be applied on entries.

Return Value

Current map with entries retained and rest removed.

Example - Retaining multiple entries from a Map of String and String

Following is an example of the usage of this method −

main.groovy

// define a map
def map = ["A" : "Apple", "B" : "Banana", "C":"Carrot" ] 

// retain entries from map whose size is more than 5 and remove others
map.retainAll{it.value.size() > 5}

println(map)

Output

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

[B:Banana, C:Carrot]

Example - Retaining multiple entries from a Map of Integer and Integer

Following is an example of the usage of this method −

main.groovy

// define map
def map = [1 : 11, 2 : 12, 3 : 13, 4: 14]

// retain even entries from map 
map.retainAll{key, value -> value % 2 == 0}

println(map)

Output

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

[2:12, 4:14]

Example - Retaining entries from a Map of Integer and Object

Following is an example of the usage of this method −

main.groovy

// define maps
def map = [1 : new Student(1, "Julie"), 2 : new Student(2, "Robert"),3 : new Student(3, "Adam")] 

// retain even entries from map 
map.retainAll{it.value.getRollNo() % 2 == 0}

println(map)

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 −

[2:[ 2, Robert ]]