CODEWITHSUNDEEP
java
Tapsi
Tapsi

Reputation: 1267

Is there possibility of sum of ArrayList without looping

Is there possibility of sum of ArrayList without looping?

PHP provides sum(array) which will give the sum of array.

The PHP code is like

$a = array(2, 4, 6, 8);
echo "sum(a) = " . array_sum($a) . "\n";

I wanted to do the same in Java:

List tt = new ArrayList();
tt.add(1);
tt.add(2);
tt.add(3);

Upvotes: 115

Views: 273952

Answers (13)

lczapski
lczapski

Reputation: 4140

This can be done with reduce using method references reduce(Integer::sum): 

Integer reduceSum = Arrays.asList(1, 3, 4, 6, 4)
        .stream()
        .reduce(Integer::sum)
        .get();

Or without Optional:

Integer reduceSum = Arrays.asList(1, 3, 4, 6, 4)
        .stream()
        .reduce(0, Integer::sum);

Upvotes: 2

msayag
msayag

Reputation: 8675

Once is out (March 2014) you'll be able to use streams:

If you have a List<Integer>

int sum = list.stream().mapToInt(Integer::intValue).sum();

If it's an int[]

int sum = IntStream.of(a).sum();

Upvotes: 202

Erhan Bagdemir
Erhan Bagdemir

Reputation: 5327

Then write it yourself:

public int sum(List<Integer> list) {
     int sum = 0; 

     for (int i : list)
         sum = sum + i;

     return sum;
}

Upvotes: 27

J&#225;n Яabčan
J&#225;n Яabčan

Reputation: 773

for me the clearest way is this:

doubleList.stream().reduce((a,b)->a+b).get();

or 

doubleList.parallelStream().reduce((a,b)->a+b).get();

It also use internal loops, but it is not possible without loops.

Upvotes: 9

yurez
yurez

Reputation: 3232

You can use GNU Trove library:

TIntList tt = new TIntArrayList();
tt.add(1);
tt.add(2);
tt.add(3);
int sum = tt.sum();

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533820

The only alternative to using a loop is to use recursion.

You can define a method like

public static int sum(List<Integer> ints) {
   return ints.isEmpty() ? 0 : ints.get(0) + ints.subList(1, ints.length());
}

This is very inefficient compared to using a plain loop and can blow up if you have many elements in the list.

An alternative which avoid a stack overflow is to use.

public static int sum(List<Integer> ints) {
    int len = ints.size();
    if (len == 0) return 0;
    if (len == 1) return ints.get(0);
    return sum(ints.subList(0, len/2)) + sum(ints.subList(len/2, len));
}

This is just as inefficient, but will avoid a stack overflow.

The shortest way to write the same thing is

int sum = 0, a[] = {2, 4, 6, 8};

for(int i: a) {
    sum += i;
}

System.out.println("sum(a) = " + sum);

prints

sum(a) = 20

Upvotes: 11

sivi
sivi

Reputation: 11144

If you know about the map function, then you know that a map is also can be recursive loop or recursive loop. But obviously you have to reach each element for that. so, I could not work out the Java 8, because some syntax mismatch but wanted a very short so this is what I got.

int sum = 0
for (Integer e : myList) sum += e;

Upvotes: 1

Hari Samala
Hari Samala

Reputation: 179

You can use apache commons-collections API.

class AggregateClosure implements org.apache.commons.collections.Closure {
        int total = 0;

        @Override
        public void execute(Object input) {
            if (input != null) {
                total += (Integer) input;
            }
        }

        public int getTotal() {
            return total;
        }
    }

Then use this closure as shown below:

public int aggregate(List<Integer> aList) {
        AggregateClosure closure = new AggregateClosure();
        org.apache.commons.collections.CollectionUtils.forAllDo(aList, closure);
        return closure.getTotal();
}

Upvotes: 2

nachokk
nachokk

Reputation: 14413

This link shows three different ways how to sum in java, there is one option that is not in previous answers using Apache Commons Math..

Example:

public static void main(String args []){
    List<Double> NUMBERS_FOR_SUM = new ArrayList<Double>(){
         {
            add(5D);
            add(3.2D);
            add(7D);
         }
    };
    double[] arrayToSume = ArrayUtils.toPrimitive(NUMBERS_FOR_SUM
            .toArray(new Double[NUMBERS_FOR_SUM.size()]));    
    System.out.println(StatUtils.sum(arrayToSume));

}

See StatUtils api

Upvotes: 0

dbrin
dbrin

Reputation: 15673

Or switch to Groovy, it has a sum() function on a collection. [1,2,3,4,5,6].sum()

http://groovy.codehaus.org/JN1015-Collections

Runs on the same JVM as your java classes.

Upvotes: 0

GauravJ
GauravJ

Reputation: 2272

ArrayList is a Collection of elements (in the form of list), primitive are stored as wrapper class object but at the same time i can store objects of String class as well. SUM will not make sense in that. BTW why are so afraid to use for loop (enhanced or through iterator) anyways?

Upvotes: 0

Nishant
Nishant

Reputation: 55866

Write a util function like

public class ListUtil{

    public static int sum(List<Integer> list){
      if(list==null || list.size()<1)
        return 0;

      int sum = 0;
      for(Integer i: list)
        sum = sum+i;

      return sum;
    }
}

Then use like 

int sum = ListUtil.sum(yourArrayList)

Upvotes: 9

Mike Kwan
Mike Kwan

Reputation: 24477

Given that a list can hold any type of object, there is no built in method which allows you to sum all the elements. You could do something like this:

int sum = 0;

for( Integer i : ( ArrayList<Integer> )tt ) {
  sum += i;
}

Alternatively you could create your own container type which inherits from ArrayList but also implements a method called sum() which implements the code above.

Upvotes: 0

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