Split a List into Two Halves in Java
Here we are given a list and the task is to split it into two news lists as one can better perceive from the below illustration as follows:
Illustration:
Methods:
- Using loops[Naive Approach]
- Using subList[] method of List class
- Using partitioningBy[] method of Collectors class
- Using Google guava Library
Let us do discuss the above-defined methods to details alongside implementing via clean java programs as follows:
Method 1: Using loops
Approach:
- Create two new empty lists and assign the first half element of the original list.
- Reset into the second empty list.
Example:
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// Java Program to Split a List into Two Sublist
// Importing required classes
import java.util.ArrayList;
import java.util.List;
// Main class
public class GFG {
// Method 1
// To split a list into two sublists in Java
public static List[] split[List list]
{
// Creating two empty lists
List first = new ArrayList[];
List second = new ArrayList[];
// Getting size of the list
// using size[] method
int size = list.size[];
// Step 1
// [First size]/2 element copy into list
// first and rest second list
for [int i = 0; i < size / 2; i++]
first.add[list.get[i]];
// Step 2
// [Second size]/2 element copy into list first and
// rest second list
for [int i = size / 2; i < size; i++]
second.add[list.get[i]];
// Returning a List of array
return new List[] { first, second };
}
// Method 2
// Main driver method
public static void main[String[] args]
{
// Creating an ArrayList of string type
List list = new ArrayList[];
// Adding elements to list object
// using add[] method
list.add["Geeks"];
list.add["Practice"];
list.add["Contribute"];
list.add["IDE"];
list.add["Courses"];
// Calling split method which return List of array
List[] lists = split[list];
// Printing specific elements of list by
// passing arguments with in
System.out.println[lists[0]];
System.out.println[lists[1]];
}
}
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Method 2: Using subList[] method of List class
It returns a view of the portion of this list between the specified index[include] to another index [exclude]. For example, let us take arbitrarily from 2 to 5, Here index 2 will include only. In case if both specified indexes are equal, the returned list is empty. The List.subList[] returned a list, so non-structural changes in the returned list.
Example:
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// Java Program to Split a List into Two SubList
// Using subList[] method of List clas
// Importing required classes
import java.util.ArrayList;
import java.util.List;
// Main class
public class GFG {
// Method 1
// To split a list into two sublists in Java
public static List[] split[List list]
{
// Finding the size of the list using List.size[]
// and putting in a variable
int size = list.size[];
// Creating new list and inserting values which is
// returned by List.subList[] method
List first
= new ArrayList[list.subList[0, [size] / 2]];
List second = new ArrayList[
list.subList[[size] / 2, size]];
// Returning an List of array
return new List[] { first, second };
}
// Method 2
// Main driver method
public static void main[String[] args]
{
// Creatingan ArrayList of String type
List list = new ArrayList[];
// Adding elements to List object
// Custom input elements
list.add["Geeks"];
list.add["Practice"];
list.add["Contribute"];
list.add["IDE"];
list.add["Courses"];
// Calling split method which return List of array
List[] lists = split[list];
// Printing specific elements of list by
// passing arguments with in
System.out.println[lists[0]];
System.out.println[lists[1]];
}
}
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[Geeks, Practice] [Contribute, IDE, Courses]
Method 3: Using partitioningBy[] method of Collectors class
Java 8 Collectors.partitioningBy[] is a method that partitions the elements of stream always in two-part, unlike Naive and List.subList[]. It returns a Collector that stores the values in a Map. The key of the map can be only in Boolean.
Syntax: partitioningBy[] method
public static Collector partitioningBy[Predicate predicate]Example:
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// Java Program to Split a List into Two Sub-List
/// Using partitioningBy[] method of Collectors class
// Importing required classes
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
// Main class
public class GFG {
// Method 1
// To split a list into two sublists in Java
public static List[] split[List list]
{
// Setting value of midIndex using comparators
int midIndex
= [[list.size[] / 2]
- [[[list.size[] % 2] > 0] ? 0 : 1]];
// Creating object of List with reference to
// ArrayList class Declaring object List
// type
List lists = new ArrayList[
list.stream[]
.collect[Collectors.partitioningBy[
s -> list.indexOf[s] > midIndex]]
.values[]];
// Returning an array containing both lists
return new List[] { lists.get[0], lists.get[1] };
}
// Method 2
// Main driver method
public static void main[String[] args]
{
// Creating an ArrayList of String type
List list = new ArrayList[];
// Adding elements to List object
// Using add[] method
list.add["Geeks"];
list.add["Practice"];
list.add["Contribute"];
list.add["IDE"];
list.add["Courses"];
// Calling split method which return List of array
List[] lists = split[list];
// Printing specific elements of list by
// passing arguments with in
System.out.println[lists[0]];
System.out.println[lists[1]];
}
}
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Method 4: Using Google guava Library
Guava is an open-source Java-based library which is developed by Google Inc. In the Guava library, we can use Lists.partition[] method that splits the list into consecutive sublists, every list specified size. In order to split the list into two sublists, In our case, we can pass the size that is equal to half the size of our list.
Example
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// Java Program to Split a List into Two Sub-List
// Importing Guava library
import com.google.common.collect.Iterables;
// Importing required classes
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
// Main class
public class GFG {
// Method 1
// To split a list into two sublists in Java
public static List[] split[List list]
{
// Partition the List into two sublists and
// getting iterator
Iterator itr
= Iterables.partition[list, [list.size[]] / 2]
.iterator[];
// Returning an array containing both lists
return new List[] { new ArrayList[itr.next[]],
new ArrayList[itr.next[]] };
}
// Method 2
// Main driver method
public static void main[String[] args]
{
// Creating an ArrayList of string type
List list = new ArrayList[];
// Adding elements t oabove object
// Custom input elements
list.add["Geeks"];
list.add["Practice"];
list.add["Contribute"];
list.add["IDE"];
list.add["Courses"];
// Calling split method which return List of array
List[] lists = split[list];
// Printing specific elements of list by
// passing arguments with in
System.out.println[lists[0]];
System.out.println[lists[1]];
}
}
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