how to perform sum/minus operation on an array of objects, based on similar values(not properties) in an array of objects [closed] Code Answer

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i have an array of objects like this:

i/p:

let payments=[ 
  {from:"b",to:"c",amount:30}, {from:"a",to:"c",amount:30},
  {from:"c",to:"a",amount:50}, {from:"b",to:"a",amount:50},
  {from:"c",to:"b",amount:66.66}, {from:"a",to:"b",amount:66.66},
  {from:"a",to:"c",amount:150}, {from:"b",to:"c",amount:150}, 
  {from:"a", to:"c",amount:75}, {from:"b", to:"c",amount:125} 
]

now i want to perform sum operation on amount property, based on same property values, and minus operation on amount property based to reverse matching property values(i,e from,to), reduce the array to :

o/p:

[
  { from: "b", to: "c", amount: 238.34 }, //(sum of all b->c amounts) minus (sum of all c->b amounts)
  { from: "a", to: "c", amount: 205 },    //(sum of all a->c amounts) minus (sum of all c-a amounts)
  { from: "a", to: "b", amount: 16.66 },  //(sum of all a->b amounts) minus (sum of all b->a amounts)
];

note: resultant array amount property shouldn’t be negative

i have tried few of the methods, but cant able to achieve this. Any help would be appreciated. Thanks

Answer

Maybe this will be helpful:

let payments=[ 
  {from:"b",to:"c",amount:30}, {from:"a",to:"c",amount:30},
  {from:"c",to:"a",amount:50}, {from:"b",to:"a",amount:50},
  {from:"c",to:"b",amount:66.66}, {from:"a",to:"b",amount:66.66},
  {from:"a",to:"c",amount:150}, {from:"b",to:"c",amount:150}, 
  {from:"a", to:"c",amount:75}, {from:"b", to:"c",amount:125} 
];

let pay = Object.entries(
  payments.reduce((tot,{from,to,amount})=>{
   let u=from+'-'+to;       // from-to-relationship (in alphabetical order)
   if (to<from) { u=to+'-'+from; amount=-amount }
   tot[u]=(tot[u]||0)+amount;  // collate all payments here
   return tot;
  }, {})
 ).map(([u,a])=>{let ft=u.split('-');
   if (a<0) {ft=ft.reverse();a=-a}
   return {from:ft[0], to:ft[1], amount:a.toFixed(2)}
 })
   
console.log(pay)

In the .reduce function I collate all payments between two partners into an accounts object with “acounts” named after “from-to” this name is always established in alphabetical order, so, if I encounter a payment {from:"b", to:"a", amount:123} I swap the order and make the amount negative:

if (to<from) { u=to+'-'+from; amount=-amount }

After having done this I walk through the accounts object with Object.entries. This will allow me to separate the account names into from and to partners again. This time I check, whether the amount payable between the partners would be negative. If so I swap the order of the partners (ft) and multiply the amonut (a) by -1:

if (a<0) {ft=ft.reverse();a=-a}
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