Ftyjtk

I have this list:

const debts = [

  {

    amount: 10,

    debtor: "Mark",

    creditor: "John"

  },

  {

    amount: 20,

    debtor: "Mark",

    creditor: "John"

  },

  {

    amount: 10,

    debtor: "Mark",

    creditor: "Tom"

   }

];

...and I want to merge the elements with the same debtor and creditor calculating the total amount, like this

const debts = [

  {

    amount: 30, // 10 + 20

    debtor: "Mark",

    creditor: "John"

  },

  {

    amount: 10,

    debtor: "Mark",

    creditor: "Tom"

   }

];

Could anyone help me? Thanks

If you're interested in a solution using Ramda, here's a suggestion:

const {

  pipe,

  mergeWithKey,

  map,

  reduce,

  values,

  groupBy,

  props,

  join

} = R;



const debts = [{

    amount: 10,

    debtor: "Mark",

    creditor: "John"

  },

  {

    amount: 20,

    debtor: "Mark",

    creditor: "John"

  },

  {

    amount: 10,

    debtor: "Mark",

    creditor: "Tom"

  }

];



const mergeAmount = mergeWithKey((key, left, right) => key === 'amount' ? left + right : left);

const groupKey = pipe(props(['debtor', 'creditor']), join(' ~> '));



const process =

  pipe(

    groupBy(groupKey),

    map(reduce(mergeAmount, {})),

    values);



console.log(process(debts));

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script>

The idea is to split the process in three steps:

1. Group debtors and creditors together


2. For each debtor/creditor group, merge the amount


3. Extract each debtor/creditor group into an array

Step 1: groupBy(groupKey)

Step 1 gets the original debts array

{

    "Mark ~> John": [

        {

            amount: 10,

            creditor: "John",

            debtor: "Mark"

        },

        {

            amount: 20,

            creditor: "John",

            debtor: "Mark"

        }

    ],

    "Mark ~> Tom": [

        {

            amount: 10,

            creditor: "Tom",

            debtor: "Mark"

        }

    ]

}

Step 2: map(reduce(mergeAmount, {}))

Step 2 gets the output from step 1

{

    "Mark ~> John": {

        amount: 30,

        creditor: "John",

        debtor: "Mark"

    },

    "Mark ~> Tom": {

        amount: 10,

        creditor: "Tom",

        debtor: "Mark"

    }

}

Step 3: values

Step 3 gets the output from step 2

[

    {

        amount: 30,

        creditor: "John",

        debtor: "Mark"

    },

    {

        amount: 10,

        creditor: "Tom",

        debtor: "Mark"

    }

]

You can use Array.reduce to create an object with key as unique pair of debtor and creditor and value as resulting object. In case there is an existing entry for the pair in object, increment the amount else add a new entry in object.

Finally, use Object.values to collect all the objects.

let debts = [{amount: 10,debtor: "Mark",creditor: "John"},{amount: 20,debtor: "Mark",creditor: "John"},{amount: 10,debtor: "Mark",creditor: "Tom"}];



let result = Object.values(debts.reduce((a,c) => {

  let key = `${c.debtor}~~${c.creditor}`;

  if(a[key]) a[key].amount += c.amount;

  else a[key] = Object.assign({},c);

  return a;

}, {}));

console.log(result);

Use the filter() function to iterate through the resulting list and check if the debtor-creditor pair already exist. If it exists, then updates the amount. Otherwise, add it as a new entry in the resulting list.

const debts = [

  {

    amount: 10,

    debtor: "Mark",

    creditor: "John"

  },

  {

    amount: 20,

    debtor: "Mark",

    creditor: "John"

  },

  {

    amount: 10,

    debtor: "Mark",

    creditor: "Tom"

  }

];



var result = 

debts.forEach((item) => {

  var existing = result.filter((resultItem, index) => {

    return resultItem.debtor === item.debtor && resultItem.creditor === item.creditor;

  });



  if (existing.length) {

    var existingIndex = result.indexOf(existing[0]);

    result[existingIndex].amount += item.amount;

  } else {

    result.push(item);

  }

})



console.log(result)