javascript - Find the sum of each row as well as that of each column in 2 dimensional matrix ( m X n) - Stack Overflow

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How to find the sum of each row as well as that of each column in 2 dimensional matrix ( m X n).

[
  [1, 2, 3],
  [3, 2, 1]
]

I know in one dimensional array, we can do:

var sum = [5, 6, 3].reduce(add, 0);

function add(a, b) {
  return a + b;
}

console.log(sum);

How to find the sum of each row as well as that of each column in 2 dimensional matrix ( m X n).

[
  [1, 2, 3],
  [3, 2, 1]
]

I know in one dimensional array, we can do:

var sum = [5, 6, 3].reduce(add, 0);

function add(a, b) {
  return a + b;
}

console.log(sum);

• javascript
• arrays

Share Improve this question Follow edited May 12, 2019 at 19:13 adiga 35.3k99 gold badges6565 silver badges8787 bronze badges asked Aug 2, 2016 at 12:49 D V YogeshD V Yogesh 3,70011 gold badge3131 silver badges4040 bronze badges 2

• 1 Possible duplication of question: stackoverflow./questions/15083103/… – GH Karim Commented Aug 2, 2016 at 12:52
• 1 duplication is not Possible ,in your above link answer is available total sum of two dimensional array, but i want row and as well as col separably,simple menting and giving down vote is not good – D V Yogesh Commented Aug 2, 2016 at 13:17

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 9

Using ECMAScript6, you can do:

var matrix = [
  [ 1, 2, 3 ],
  [ 7, 2, 6 ]
];

// sums of rows
var rowSum = matrix.map(r => r.reduce((a, b) => a + b));

// sums of columns
var colSum = matrix.reduce((a, b) => a.map((x, i) => x + b[i]));

console.log(rowSum);
console.log(colSum);

The sum of rows is rather easy to illustrate. Let's consider a 3x3 matrix which is easier to format here:

[ 1 2 3 ] -- reduce --> 6  \
[ 7 2 6 ] -- reduce --> 15  } -- map --> [ 6, 15, 7 ]
[ 4 1 2 ] -- reduce --> 7  /

The sum of columns is less trivial. We 'reduce' by 'mapping' 2 rows at a time:

      [ 1 2 3 ]                     [ 8 4 9 ]
    + [ 7 2 6 ]   -- reduce -->   + [ 4 1 2 ]
      ---------                     ---------
map = [ 8 4 9 ]              map = [ 12 5 11 ]

The follwoing code is showing two examples using map

The first sums the 2D array horizontally.

    var array = [ [1,2,3], [3,2,1] ];
    var sum= array.map( function(row){
      return row.reduce(function(a,b){ return a + b; }, 0);
    });

The second sums the 2D array vertically.

var array = [ [1,2,3], [3,2,1] ];
var sum2= array.map(function(row, i) {
  return array.map(function(row) {
    return row[i]; }
  ).reduce(function(a, b) {
    return a+b;
  }, 0);
});

Check working example

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