How to access an inner arrays element using a for loop in javascript [duplicate]

Question

I have a function that accepts an array of arrays as an argument and i need to get access to a specific element of the inner array to push it to a locally scoped empty array, so that i can use reduce method to return a net total.

I can get access using the map method of the specific element in the inner array and push these elements to an array but i can not seem to achieve this using a standard for loop.

// here is the array and i require access to the totals

var finances = [
  ["Jan-2010", 884],
  ["Feb-2010", 655],
  ["Mar-2010", 1013],
  ["Apr-2010", 417],
  ["May-2010", -7503],
  ["Jun-2010", 857],
  ["Jul-2010", 3096],
  ["Aug-2010", 885],
  ["Sep-2010", -6386],
  ["Oct-2010", 532],
  ["Nov-2010", 3810],
];

function netTotal(financeArray) {
  // lets create a variable here to return the net total to the function

  let net;

  // lets create an empty array here to store all the totals to use with reduce method

  let totals = [];

  // we need to loop through the array and push element to the totals array

  for (let i = 0; i < financeArray.length; i++) {
    let innerArrayLength = financeArray[i].length;

    for (let j = 0; j < innerArrayLength; j++) {
      totals.push(financeArray[i][j]);
    }
  }

  // lets use the reduce method to return the net total

  // return (net = totals.reduce((prev, next) => prev + next));

  // returning the totals array to check what is pushed to this array

  return totals;
}


console.log(netTotal(finances));

// output to console 

Array(22) [ "Jan-2010", 884, "Feb-2010", 655, "Mar-2010", 1013, "Apr-2010", 417, "May-2010", -7503, … ]

The totals array should be a flat array with all the amounts as elements so reduce can work to total every amount instead running the above function i get 22 elements in a single array because the original array is 11 arrays within the outer array.

How can i use the for loop to get access to only the amounts and push each element to this new empty array.

Any help much appreciated..

ditch the inner for loop and do totals.push(financeArray[i][1] instead? Or using Array.map let totals = financeArray.map(x => x[1])? Or use Array.reduce directly: let net = financeArray.reduce((a, c) => a + c[1], 0)? — derpirscher
– derpirscher, Commented Dec 29, 2022 at 12:14

Xephoriath · Accepted Answer · 2022-12-29 12:28:20Z

0

Your nested for loops cause all elements of the arrays to be pushed. Replace them with:

for (let i = 0; i < financeArray.length; i++) {
    let innerArray = financeArray[i];
    let amount = innerArray[1]; 
    totals.push(amount);
}

Setting amount = innerArray[1] ensures you only grab the amounts and not unnecessary elements.

answered Dec 29, 2022 at 12:28

Xephoriath

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1 Comment

Sho.ayb Over a year ago

thanks this is the accepted answer because i wanted to see if this can be achieved using a for loop rather than the map or flatmap methods.

emy · Accepted Answer · 2022-12-29 12:46:01Z

0

You can use flatMap method.

totals = financeArray.flatMap(f => f[1]);
const total = totals.reduce((prev, curr) => prev + curr, 0);

MDN: flatMap()

edited Dec 29, 2022 at 12:46

answered Dec 29, 2022 at 12:40

emy

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1 Comment

derpirscher Over a year ago

You don't need flatMap for that, a simple map is just fine (at least in OP's case)

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