Is there possibility of sum of ArrayList without looping

Question

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);

What if the `ArrayList` doesn not contain something that is "summable"? ArrayList and an array isn't necessarily the same thing. As for summing numbers in an array, that's a very simple for loop over the elements and calculating a cumulative sum. — posdef, May 11 '11 at 12:02
The PHP function `array_sum` also does a loop internally, it just hides it from the user. — Paŭlo Ebermann, May 11 '11 at 13:01
It's a reasonable question. After all, it's nearly as trivial to write a loop to find the largest element in a list, yet java.util.Collections provides a max() method. — John Velonis, Mar 13 '14 at 21:08
Very reasonable question, after all, that's the point of methods, right? Reuse :) — Ben Taliadoros, Jul 25 '14 at 15:11
I suggest the answer provided by Ján Яabčan. I don't know why his answer isn't the most upvoted one, since it provides the most clear and objetive method to accomplish your sum. — Pelicer, Jun 29 '21 at 10:40

score 192 · Answer 1 · edited Apr 19 '18 at 05:30

192

Once java-8 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();

edited Apr 19 '18 at 05:30

Basil Bourque

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answered Jul 24 '13 at 23:25

msayag

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`map` uses loops implicitly – Nikos M. Aug 19 '15 at 16:08
10

You could use recursion to not use a loop. :D (don't do this) – Caleb Fenton Dec 09 '16 at 04:37
stream is too much slow, shit... – xiaoweiz Feb 03 '23 at 18:01

score 27 · Answer 2 · edited Dec 06 '16 at 17:34

27

Then write it yourself:

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

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

     return sum;
}

edited Dec 06 '16 at 17:34

Community

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answered May 11 '11 at 12:01

Erhan Bagdemir

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Or extending ArrayList with the sum method so you have it built in to your own ArrayList. – Bueller May 11 '11 at 12:03
3

When doing the actual addition, it's just nicer to use a simple `int`. There is little value in using `Integer` with java's auto-boxing features here. Also, you are creating and recreating potentially many new `Integer` objects each time, since it is an `Immutable` type. – Java Drinker May 11 '11 at 12:37

score 11 · Answer 3 · edited Jun 28 '15 at 00:10

11

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

edited Jun 28 '15 at 00:10

Mel Kicchi

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answered May 11 '11 at 12:47

Peter Lawrey

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In the code you miss the call to sum() in the first recursive definition. The second recursive definition does not prevent stack overflow from happening, it makes it less likely. – Teudimundo Dec 03 '15 at 13:47
1

@Teudimundo True, While it doesn't prevent it, the maximum size of a List is Integer.MAX_VALUE and the log2 is 31 which is maximum depth. Most systems have many thousands of calls as a limit but if you are very close to the this it could still blow. – Peter Lawrey Dec 03 '15 at 14:02

score 9 · Answer 4 · answered May 11 '11 at 12:02

9

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)

answered May 11 '11 at 12:02

Nishant

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but how can i do it for long value in arraylist ? – Ravi Parmar Aug 23 '11 at 17:59

score 8 · Answer 5 · answered Apr 04 '16 at 17:30

8

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.

answered Apr 04 '16 at 17:30

Ján Яabčan

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This is the most clear and objetive answer for this kind of operation. – Pelicer Jun 29 '21 at 10:38

score 2 · Answer 6 · answered Oct 22 '14 at 17:28

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();
}

lczapski · Answer 7 · 2020-03-10T19:51:20.147

2

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);

edited Mar 10 '20 at 19:51

answered Mar 10 '20 at 08:34

lczapski

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score 1 · Answer 8 · answered Mar 03 '15 at 17:15

1

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;

answered Mar 03 '15 at 17:15

sivi

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You are right. I said it's a minimal loop instead of map which can be tail recursive. – sivi Apr 04 '15 at 07:42
"Is there possibility of sum of ArrayList without looping" – alexander Oct 05 '16 at 13:01

score 0 · Answer 9 · answered Jul 24 '13 at 23:31

0

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.

answered Jul 24 '13 at 23:31

dbrin

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Yeah. Sum function is definitely reason to switch to another language. :D – ruX Mar 18 '14 at 12:48
1

The question is tagged `Java`, so this is technically not a valid answer. – Bengt Dec 17 '14 at 01:16

score 0 · Answer 10 · answered Oct 08 '14 at 20:14

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

score 0 · Answer 11 · answered Jul 30 '15 at 14:36

0

You can use GNU Trove library:

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

answered Jul 30 '15 at 14:36

yurez

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score 0 · Answer 12 · answered May 11 '11 at 12:02

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.

score 0 · Answer 13 · answered May 11 '11 at 12:05

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?

Is there possibility of sum of ArrayList without looping

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