Creating an array of object with cumulative sum dynamically in javascript-CodePudding

I have array of objects like this and require to calculate running total(accumulate sum) dynamically for N keys.

  let a = [
  {"subject":  "Civil", "a": 100, "b":50, "c":100 },
  {"subject":  "aero",  "a": 200, "b":130,"c":100 },
  {"subject":  "tribe", "a": 100, "b":100,"c":600 },
  {"subject":  "solen", "a": 400, "b":150,"c":100},
  {"subject":  "space", "a": 100, "b":100,"c":900 }
];

Required Output as below :

[
{"subject": "Civil", "a": 100, "b": 50,  "c": 100},
{"subject": "aero",  "a": 300, "b": 180, "c": 200},
{"subject": "tribe", "a": 400, "b": 280, "c": 800},
{"subject": "solen", "a": 800, "b": 430, "c": 900},
{"subject": "space"," a": 900, "b": 530, "c": 1800}]

I tried below using MAP as below :

let b = a.map( x => ({...x,"a":a1 =x.a,"b":b1 =x.b,"c":c1 =x.c}) )

I want to achieve it dynamically without writing a, b, c.

CodePudding user response：

If you want to cumulatively sum every property other than subject, you can do so by mapping the array to new values, keeping an object reference for each running total as you go

const a = [{"subject":"Civil","a":100,"b":50,"c":100},{"subject":"aero","a":200,"b":130,"c":100},{"subject":"tribe","a":100,"b":100,"c":600},{"subject":"solen","a":400,"b":150,"c":100},{"subject":"space","a":100,"b":100,"c":900}]

const cf = {} // store running totals in here
const b = a.map(({ subject, ...props }) => ({
  subject,
  ...Object.fromEntries(Object.entries(props).map(([ key, val ]) => [
    key,
    cf[key] = (cf[key] ?? 0)   val // value is the result of the assignment
  ]))
}))

console.log(b)

.as-console-wrapper { max-height: 100% !important; }

CodePudding user response：

You can use a combination of .map(), .slice() and .reduce() array methods as follows:

let a = [
  {"subject":  "Civil", "a": 100, "b":50, "c":100 },
  {"subject":  "aero",  "a": 200, "b":130,"c":100 },
  {"subject":  "tribe", "a": 100, "b":100,"c":600 },
  {"subject":  "solen", "a": 400, "b":150,"c":100},
  {"subject":  "space", "a": 100, "b":100,"c":900 }
];

let b = a.map((x,i) => ({
    subject:x.subject,
    a:a.slice(0,i 1).map(({a}) => a).reduce((x,y) => x   y),
    b:a.slice(0,i 1).map(({b}) => b).reduce((x,y) => x   y),
    c:a.slice(0,i 1).map(({c}) => c).reduce((x,y) => x   y)
}));

console.log( b );