Is there a way to use : to add a range of values in an array?-CodePudding

I have an array and I am trying to sum the values of just a portion of the array.

For example my array is [1,2,3,4,5,6], but I want to add the values only to the third element

[1,2,3]. I thought I used a method involving the semi colon before, but I cant remember for sure.

something like int sum = Sum (arr[0]:arr[2]) but I am not sure. Does something like this exist?

I think I used it in Python a few years ago.

CodePudding user response：

There is no built in method to sum up a sub array. The simplest way could be to stream over the sub array:

int[] myArray = {1,2,3,4,5,6};

int sum = Arrays.stream(myArray, 0, 3).sum();

where 0 and 3 are the start and end indices (Start inclusiv, end exclusiv)

CodePudding user response：

Extending Eritrean's excellent answer you can create an interface with a meaningful name and tuck it away in your library.

interface IntRangeSum {
    static public int apply(int[] a, int start, int end) {
         return Arrays.stream(a, start, end).sum();
    }
}


int[] a = {1,2,3,4,5};
int result = IntRangeSum.apply(a, 2, 4);
System.out.println(result);

prints

CodePudding user response：

You're looking for the slicing notation [start:stop:step]

values = [1,2,3,4,5,6]
s = sum(values[:3])

CodePudding user response：

import java.util.*;
public class MyClass {
    public static void main(String args[]) {
      int[] oldArray ={1,2,3,4,5};
      int[] newArray = Arrays.copyOfRange(oldArray, 0, 3);
      int sum = 0;
      for (int i: newArray) {
        sum  = i;
      }
      System.out.println("Sum = "   sum);
    }
}

Output: 6

As far as I know Java doesn't have the slicing notation you know from Python, but this, while more verbose, should do the trick.

CodePudding user response：

You could use the appropriate variant of java.util.Arrays.copyOfRange methods to create and operate on a slice.

Or use a loop:

int sum = 0;
for(var i=0; i < 3; i  ) {
  sum = sum   i
}

CodePudding user response：

Another option would be to use combination Arrays.stream() IntStream.limit():

int[] arr = // initializing the array

int sum = Arrays.stream(arr).limit(3).sum();