getting total from each item in an object-CodePudding

How do we map and object and add certain values and then get the total, I wanted to map the object below and then and items from the object. Anyone has an idea ?

Object:

  [
    {
        "description": "Current Term",
        "monthlyRent": 29971.599999999995,
        "monthsInPeriod": 41.7,
        "rentInPeriod": null
    },
    {
        "description": "Current Term - Rent Adjustment",
        "monthlyRent": 31470.180000000004,
        "monthsInPeriod": 47.96666666666667,
        "rentInPeriod": 1509519.634
    }
]
29971.599999999995   41.7   = 30,012
31470.180000000004   47.96666666666667 =  31,517

Result: should be

 total = 30,012   31,517

CodePudding user response：

You can use map and reduce to get the desired result:

const data = [
    {
        "description": "Current Term",
        "monthlyRent": 29971.599999999995,
        "monthsInPeriod": 41.7,
        "rentInPeriod": null
    },
    {
        "description": "Current Term - Rent Adjustment",
        "monthlyRent": 31470.180000000004,
        "monthsInPeriod": 47.96666666666667,
        "rentInPeriod": 1509519.634
    }
];
const total = data
  .map(item => item.monthlyRent * item.monthsInPeriod)
  .reduce((currentValue, acc) => acc   currentValue);

I don't actually understand why would you want to add the monthlyRent and the monthsInPeriod so I multiplied them instead (to get the amount of money that needs to be payed during the number of months). If you want to add them like in your question, just replace the map with item.monthlyRent item.monthsInPeriod.

CodePudding user response：

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array. Refer the sample here.

The reduce() method executes a user-supplied “reducer” callback function on each element of the array, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the array is a single value. Refer the sample here.

By combining both you can come up with solution like this:

let arry = [
    {
        "description": "Current Term",
        "monthlyRent": 29971.599999999995,
        "monthsInPeriod": 41.7,
        "rentInPeriod": null
    },
    {
        "description": "Current Term - Rent Adjustment",
        "monthlyRent": 31470.180000000004,
        "monthsInPeriod": 47.96666666666667,
        "rentInPeriod": 1509519.634
    }
];

let total = arry 
  .map(obj=> obj.monthlyRent   obj.monthsInPeriod)
  .reduce((value, previousValue) => previousValue   value);

Another solution is to use simple for each:

 let total2:number=0;
    for (let i = 0; i < this.arry.length; i  ) {
       let val = this.arry[i].monthlyRent   this.arry[i].monthsInPeriod;
       total2 = total2 val       
    }

Please find the attached StackBlitz here.