Creating an array of arrays without duplicates to add values

August 18, 2022

I have an array of objects with number values that I am trying to loop over to get a result of and ARRAY of ARRAYS. Ive found examples of using for loop where the output is an ARRAY of OBJECTS. But I am having trouble looping over and adding the number values to create an array for each month value with the second value being a total of all the values listed for that month.

var input = [
  {month: "Jan", value: 3},
  {month: "Jan", value: 3.5},
  {month: "Feb", value: 2.1},
  {month: "Mar", value: 6},
  {month: "Apr", value: 4.3},
  {month: "May", value: 5.5},
  {month: "Jun", value: 7},
  {month: "Jun", value: 9},
  {month: "Jul", value: 7},
  {month: "Jul", value: 9},
  {month: "Jul", value: 7},
  {month: "Aug", value: 9},
  {month: "Sep", value: 9},
  {month: "Sep", value: 9},
  {month: "Oct", value: 8},
  {month: "Oct", value: 5},
  {month: "Oct", value: 3},
  {month: "Nov", value: 12},
  {month: "Nov", value: 19.5},
];

var result = [];

for (var i = 0; i < input.length; i++) {
  var data = input[i];
  var found = false;
  console.log(result[1][1], "help");
  for (var j = 0; j < result.length; j++) {
    if (result[j].month === data.month) {
      found = true;

      result[j][1] += data.value;
      break;
    }
  }
  if (!found) {
    result.push([data.month, data.value]);
  }
}

Currently returns an array of arrays but it is not adding the values instead it is making an array for each object.

My expected output would be:

[["Jan", 6.5],["Feb", 2.1],["Mar", 6],["Jun", 16]...etc]

>Solution :

An alternate approach using month as keys in an Object.

var input = [
  { month: "Jan", value: 3 },
  { month: "Jan", value: 3.5 },
  { month: "Feb", value: 2.1 },
  { month: "Mar", value: 6 },
  { month: "Apr", value: 4.3 },
  { month: "May", value: 5.5 },
  { month: "Jun", value: 7 },
  { month: "Jun", value: 9 },
  { month: "Jul", value: 7 },
  { month: "Jul", value: 9 },
  { month: "Jul", value: 7 },
  { month: "Aug", value: 9 },
  { month: "Sep", value: 9 },
  { month: "Sep", value: 9 },
  { month: "Oct", value: 8 },
  { month: "Oct", value: 5 },
  { month: "Oct", value: 3 },
  { month: "Nov", value: 12 },
  { month: "Nov", value: 19.5 },
];

const totalMonthObj = {};
for (monthObj of input) {
  if (totalMonthObj[monthObj.month]) {
    totalMonthObj[monthObj.month].value += monthObj.value;
  } else {
    totalMonthObj[monthObj.month] = monthObj;
  }
}
console.log(Object.values(totalMonthObj).map(({month,value})=>[month,value]));