Javascript Multiplying Within an Array-CodePudding

I have an array with multiple arrays inside. I would like to multiply the contents of each array.

Here is my code--currently not getting anything in console. The desired output is 3 numbers-- the result of multiplication of the three arrays

var arr = [
  [1, 2, 3],
  [3, 4],
  [7, 8, 9]
]
var mult = 1
for (i = 0; i < arr.length; i  ) {
  for (j = 0; j < arr.length; j  ) {
    mult *= arr[i][j]
  }
  console.log(mult)
}

CodePudding user response：

You could map the result of the nested multiplying.

const
    multiply = (a, b) => a * b,
    array = [[1, 2, 3], [3, 4], [7, 8, 9]],
    result = array.map(a => a.reduce(multiply, 1));

console.log(result);

CodePudding user response：

You can try this, it is easier using map and reduce functions. arr.map(array => array.reduce(arrayMult, 1)) is the multiplication of each inner array, like [ 6, 12, 504 ], and the last reduce is to multiply these values.

var arr = [[1, 2, 3],[3, 4],[7, 8, 9]];
const arrayMult = (prev, curr) => prev * curr;
const total = arr.map(array => array.reduce(arrayMult, 1)).reduce(arrayMult, 1);

CodePudding user response：

You should iterate over rows. So you need to change inner loop on this :

for (j = 0; j < arr[i].length; j )

const array = [
  [1, 2, 3],
  [3, 4],
  [7, 8, 9]
];

for (i = 0; i < array.length; i  ) {
let result = 1;
  for (j = 0; j < array[i].length; j  ) {
    result *= array[i][j]
  }
  console.log(result);
}

CodePudding user response：

Nothing wrong with good old iterating; your existing approach only had one bug, on the inner loop you were still checking the length of the top-level array instead of the inner array; j should range from 0 to arr[i].length, not arr.length.

An alternative approach uses map and reduce; comments below explain how it works:

var arr = [
  [1, 2, 3],
  [3, 4],
  [7, 8, 9]
]

console.log(
  arr.map(a => {  // <-- calls a function on each element of arr, 
                  // leaving the results in an array
    return a.reduce( // <-- reducer is like map, calling a function 
                     // on each element of a,  but collects its results
                     // in a "collector" variable passed to each step
      (val, sum) => {return val * sum}, // <-- multiply this value with 
                                        // the ones so far
      1 // <-- initial value for the collector
    )
  })
)

CodePudding user response：

One approach was to iterate the array of arrays via map which for each array puts the product of all of its items where the latter gets achieved via a multiplying reduce task.

console.log([

  [1, 2, 3],
  [3, 4],
  [7, 8, 9],

].map(arr =>
  arr.reduce((x, y) => x * y)
));