How to Filter a Map Based on Values in Java - Step by Step Examples

How to Filter a Map Based on Values in Java ?

Answer

To filter a map based on values in Java, you can iterate over the map entries and add key-value pairs that meet the filter criteria to a new map. This method allows you to create a subset of the original map based on specific value conditions.

✐ Examples

1 Filtering a Map Based on Value Range

We can filter a map based on a range of values in Java by iterating over the map entries and adding key-value pairs that fall within the specified range to a new map.

For example,

We start by importing the java.util.HashMap and java.util.Map classes, which provide the necessary functions and data structures for working with maps.
We declare and initialize a HashMap named myMap with some key-value pairs. In this example, the map has integer keys and integer values.
We declare an empty map named filteredMap to store the filtered key-value pairs.
We define the lower and upper bounds of the value range.
We iterate over the original map entries using a for loop and check if each value falls within the specified range.
We add the key-value pairs that meet the condition to the filteredMap.
We print the filtered map to the console using the System.out.println function to verify the filtering.

Java Program

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, Integer> myMap = new HashMap<>();
        myMap.put(1, 10);
        myMap.put(2, 20);
        myMap.put(3, 30);
        myMap.put(4, 40);
        myMap.put(5, 50);

        // Declare an empty map to store the filtered key-value pairs
        Map<Integer, Integer> filteredMap = new HashMap<>();

        // Define the value range
        int lowerBound = 20;
        int upperBound = 40;

        // Iterate over the original map and filter based on the value range
        for (Map.Entry<Integer, Integer> entry : myMap.entrySet()) {
            if (entry.getValue() >= lowerBound && entry.getValue() <= upperBound) {
                filteredMap.put(entry.getKey(), entry.getValue());
            }
        }

        // Print the filtered map
        System.out.println("Filtered Map by Value Range: " + filteredMap);
    }
}

Output

Filtered Map by Value Range: {2=20, 3=30, 4=40}

2 Filtering a Map Based on Specific Values

We can filter a map based on specific values in Java by iterating over the map entries and adding key-value pairs that match the specified values to a new map.

For example,

We start by importing the java.util.HashMap, java.util.HashSet, and java.util.Map classes, which provide the necessary functions and data structures for working with maps and sets.
We declare and initialize a HashMap named myMap with some key-value pairs. In this example, the map has integer keys and integer values.
We declare an empty map named filteredMap to store the filtered key-value pairs.
We define a set of specific values that we want to filter the map by.
We iterate over the original map entries using a for loop and check if each value matches one of the specified values.
We add the key-value pairs that meet the condition to the filteredMap.
We print the filtered map to the console using the System.out.println function to verify the filtering.

Java Program

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, Integer> myMap = new HashMap<>();
        myMap.put(1, 10);
        myMap.put(2, 20);
        myMap.put(3, 30);
        myMap.put(4, 40);
        myMap.put(5, 50);

        // Declare an empty map to store the filtered key-value pairs
        Map<Integer, Integer> filteredMap = new HashMap<>();

        // Define the specific values to filter by
        Set<Integer> valuesToFilter = new HashSet<>();
        valuesToFilter.add(10);
        valuesToFilter.add(30);
        valuesToFilter.add(50);

        // Iterate over the original map and filter based on the specific values
        for (Map.Entry<Integer, Integer> entry : myMap.entrySet()) {
            if (valuesToFilter.contains(entry.getValue())) {
                filteredMap.put(entry.getKey(), entry.getValue());
            }
        }

        // Print the filtered map
        System.out.println("Filtered Map by Specific Values: " + filteredMap);
    }
}

Output

Filtered Map by Specific Values: {1=10, 3=30, 5=50}

3 Filtering a Map with String Values Based on Prefix

We can filter a map with string values based on a specific prefix in Java by iterating over the map entries and adding key-value pairs that have values starting with the given prefix to a new map.

For example,

We start by importing the java.util.HashMap and java.util.Map classes, which provide the necessary functions and data structures for working with maps.
We declare and initialize a HashMap named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We declare an empty map named filteredMap to store the filtered key-value pairs.
We define a prefix string that we want to filter the map by.
We iterate over the original map entries using a for loop and check if each value starts with the specified prefix.
We add the key-value pairs that meet the condition to the filteredMap.
We print the filtered map to the console using the System.out.println function to verify the filtering.

Java Program

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, String> myMap = new HashMap<>();
        myMap.put(1, "apple");
        myMap.put(2, "banana");
        myMap.put(3, "apricot");
        myMap.put(4, "carrot");
        myMap.put(5, "blueberry");

        // Declare an empty map to store the filtered key-value pairs
        Map<Integer, String> filteredMap = new HashMap<>();

        // Define the prefix to filter by
        String prefix = "ap";

        // Iterate over the original map and filter based on the prefix
        for (Map.Entry<Integer, String> entry : myMap.entrySet()) {
            if (entry.getValue().startsWith(prefix)) {
                filteredMap.put(entry.getKey(), entry.getValue());
            }
        }

        // Print the filtered map
        System.out.println("Filtered Map by Prefix: " + filteredMap);
    }
}

Output

Filtered Map by Prefix: {1=apple, 3=apricot}

Summary

In this tutorial, we learned How to Filter a Map Based on Values in Java language with well detailed examples.

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How to Filter a Map Based on Values in Java - Step by Step Examples