How do I write all iterations of reduce to an array?-CodePudding

The idea behind the script is as follows: I am filtering the original array by removing all even values from it. Next, I form a new array from the partial products of the original array:

// new first element = 1 * 3;
// second = (first (previous multiplication) * current value) = 3 * 3 (9);
// third = (previous product * current value) = 9 * 9 (81)

I got the results I wanted, but my output doesn't look like an array:

Input:
3 3 9

Output:
3
9
81

Please help me draw the following output:

Input:
3 3 9

Output:
3 9 81

function modify(arr) {
  var result = [];

  arr = arr.filter(item => !(item % 2 == 0))
    .reduce(function(acc, curItem) {
      console.log(acc * curItem);
      return acc * curItem;
    }, 1)

  for (let i = 0; i < result.length; i  ) {
    arr.push(result[i]);
  };
  return result;
}

console.log( modify([3,3,9]) )

CodePudding user response：

You can use reduce keeping track of both your cumulative product, and the final array:

const input = [3, 3, 9];

const output = input.reduce( (acc,val) => {
   const newResult = acc.cum * val;
   acc.result.push(newResult);
   acc.cum = newResult;
   return acc;
},{cum:1, result:[]});

console.log(output.result);

As the last element of the array is always the cumulative product, you could also write it like this:

const input = [3, 3, 9];

const output = input.reduce( (acc,val) => {
   const newResult = (acc.length ? acc[acc.length-1] : 1) * val;
   acc.push(newResult);
   return acc;
},[]);

console.log(output);

It's up to you which one of these you find easier to work with.

CodePudding user response：

With Array#reduce() method and the spread operator you can transform your array as in the following demo:

let modify = (arr) => arr.reduce((acc,cur,i) => [...acc, (acc[i-1] || 1) * cur],[]);

console.log( modify([3,3,9]) );

Or simply:

function modify(arr) {
    return arr.reduce(function(acc,cur,i) { 
        return [...acc, (acc[i-1] || 1) * cur] 
    }, []);
}

console.log( modify([3,3,9]) );

Or if this is code that runs once, in which case you don't need a function:

let oldArray = [3,3,9];

let newArray = oldArray.reduce(function(acc,cur,i) { 
    return [...acc, (acc[i-1] || 1) * cur] 
}, []);

console.log( newArray );