How to derive new objects value from two different arrays in Javascript

Question

I have two arrays as below,

var day1 = [{id: 1, type:"20H", cases: 30, fail: 5},
                {id: 1, type:"12C", cases: 10, fail: 3},
                {id: 1, type:"4B", cases: 20, fail: 8}];
              
var day5 = [{id: 5, type:"12C" ,cases: 5, fail: 2},
             {id: 5, type:"4B", cases: 12, fail: 3},
             {id: 5, type:"20H", cases: 20, fail: 6}];

Expecting the below result of array,

var result = [{id: 1, type:"20H", caseCount: 30, failCount: 5, difference: 10, diffPercentage: 50.00},
              {id: 1, type:"12C", caseCount: 10, failCount: 3, difference: 5, diffPercentage: 100.00},
              {id: 1, type:"4B", caseCount: 20, failCount: 8, difference: 8, diffPercentage: 66.66}];

The logic of difference and diffPercentage as below,

Here, I am not getting how to get the matched value between two arrays and proceed.

if(day1.type === day5.type){
    difference = day1.cases - day5.cases;//Here, 30-20 = 10
    diffPercentage = ((day1.cases - day5.cases)/(day5.cases)*100).toFixed(2);// 10/20 * 100 = 50.00
}

Tried the following,

result = [];

day1.forEach(function(day1Items, idx){
    var day5Items = day5[idx];
    var outputElements = {};
    if(day1Items && day5Items){            
      if(day1Items.type == day5Items.type)){ //Here, I am not getting how to get the matched value between two array and proceed.
        console.log("Inside if block2"); //it is coming here, because, the if condition going index wise check
        outputElements.id = day1Items.id;
        outputElements.type = day1Items.type;
        outputElements.caseCount = day1Items.cases;
        outputElements.failCount = day1Items.fail;
        outputElements.difference = day1Items.cases - day5Items.cases;//Here, I need to get the cases value respective type matched
        outputElements.diffPercentage = ((day1.cases - day5.cases)/(day5.cases)*100).toFixed(2);
        result.push(outputElements);
      }
    }
});

console.log(result);

Vikram Patil · Accepted Answer · 2021-08-11 05:06:03Z

You can use a Map to achieve this.

    var day1 = [
          { id: 1, type: "20H", cases: 30, fail: 5 },
          { id: 1, type: "12C", cases: 10, fail: 3 },
          { id: 1, type: "4B", cases: 20, fail: 8 }
     ];

     var day5 = [
          { id: 5, type: "12C", cases: 5, fail: 2 },
          { id: 5, type: "4B", cases: 12, fail: 3 },
          { id: 5, type: "20H", cases: 20, fail: 6 }
     ];


     function merge(arr1, arr2) {
       const hashMap = new Map();
       arr1.forEach((elem) => {
       const elemClone = {
         ...elem,
         failCount: elem.fail,
         caseCount: elem.cases
       };
       delete elemClone.fail;
       delete elemClone.cases;
       hashMap.set(elem.type, elemClone);
     });

     arr2.forEach((elem) => {
       if (hashMap.has(elem.type)) {
         const difference = Math.abs(elem.cases -
           hashMap.get(elem.type).caseCount);
         const diffPercentage = Number(parseFloat((difference / elem.cases) 
           * 100).toFixed(2));
         hashMap.set(elem.type, {
           ...hashMap.get(elem.type),
           difference,
           diffPercentage
          });
        } else {
          hashMap.set(elem.type, elem);
        }
      });

     return Array.from(hashMap.values());
   }

console.log(merge(day1, day5));

Raju Ahmed · Accepted Answer · 2021-08-11 05:54:29Z

1

This should work:

 var day1 = [{id: 1, type:"20H", cases: 30, fail: 5},
                    {id: 1, type:"12C", cases: 10, fail: 3},
                    {id: 1, type:"4B", cases: 20, fail: 8}];
              
    var day5 = [{id: 5, type:"12C" ,cases: 5, fail: 2},
                 {id: 5, type:"4B", cases: 12, fail: 3},
                 {id: 5, type:"20H", cases: 20, fail: 6}];
    
        let result = []
        
        day1.forEach(d1 => {
            const day5Item = day5.find(d5 => d5.type === d1.type);
            if(day5Item){
                let difference = d1.cases - day5Item.cases;
                let diffPercentage = (difference/day5Item.cases*100).toFixed(2)
        
                result.push({
                    id:d1.id,type:d1.type,caseCount:d1.cases,failCount:d1.fail,difference,diffPercentage
                })
            }
        });
        
        console.log(result);

edited Aug 11, 2021 at 5:54

answered Aug 11, 2021 at 5:00

Raju Ahmed

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2 Comments

Vadivel A Over a year ago

Thank you Raju Ahmed. with reduce() also, I learned from you. One small note. result.push one additional comma is there which makes an uncaught syntax error. I corrected my side.

Raju Ahmed Over a year ago

sorry, I tapped twice maybe. I edited the code. and you are welcome.

Nitheesh · Accepted Answer · 2021-08-11 10:41:01Z

1

Here is the corrected version of your code.

The issue with your code was, you were looping through day1 array with array.forEach and by making use of that index you were selecting matching node from day5 array. Thats worng, This will work only if the arays are in the same order with type. Rather that selecting with var day5Items = day5[idx]; you have to select the node from day5 using Array.find and checking with type. Thil will give you the desired node.

Also there was an error in calculating diffPercentage

Instead of outputElements.diffPercentage = ((day1.cases - day5.cases)/(day5.cases)*100).toFixed(2); It should be outputElements.diffPercentage = ((day1Items.cases - day5Items.cases)/(day5Items.cases)*100).toFixed(2);. day1 and day5 are arrays. You cannot access day1.cases or day5.cases instead it should be day1Items.cases and day5Items.cases

var day1 = [
    { id: 1, type: "20H", cases: 30, fail: 5 },
    { id: 1, type: "12C", cases: 10, fail: 3 },
    { id: 1, type: "4B", cases: 20, fail: 8 }
];

var day5 = [
    { id: 5, type: "12C", cases: 5, fail: 2 },
    { id: 5, type: "4B", cases: 12, fail: 3 },
    { id: 5, type: "20H", cases: 20, fail: 6 },
];
const result = [];

day1.forEach(function(day1Items, idx){
    // You cannot simply select with index.
    // Instead make use of `Array.find` to select the node from day5 Array with the condition
    // var day5Items = day5[idx];
    var day5Items = day5.find((node) => node.type === day1Items.type)
    var outputElements = {};
    if(day1Items && day5Items){            
      if(day1Items.type == day5Items.type){ //Here, I am not getting how to get the matched value between two array and proceed.
        outputElements.id = day1Items.id;
        outputElements.type = day1Items.type;
        outputElements.caseCount = day1Items.cases;
        outputElements.failCount = day1Items.fail;
        outputElements.difference = day1Items.cases - day5Items.cases;//Here, I need to get the cases value respective type matched
        // Calculation was wrong here
        outputElements.diffPercentage = ((day1Items.cases - day5Items.cases)/(day5Items.cases)*100).toFixed(2);
        result.push(outputElements);
      }
    }
});

console.log(result);

Simplified Method

Use Array.reduce

var day1 = [
  { id: 1, type: "20H", cases: 30, fail: 5 }, 
  { id: 1, type: "12C", cases: 10, fail: 3 }, 
  { id: 1, type: "4B", cases: 20, fail: 8 }, 
  { id: 1, type: "49B", cases: 20, fail: 8 } 
];;

var day5 = [
  { id: 5, type: "12C", cases: 5, fail: 2 },
  { id: 5, type: "4B", cases: 12, fail: 3 },
  { id: 5, type: "20H", cases: 20, fail: 6 },
];

const result = day1.reduce((acc, curr) => {
  const insertNode = { id: curr.id, type: curr.type, caseCount: curr.cases, failCount: curr.fail };
  const d5Node = day5.find((node) => node.type === curr.type);
  if (d5Node) {
    insertNode.difference = curr.cases - d5Node.cases;
    insertNode.diffPercentage = (insertNode.difference / d5Node.cases * 100).toFixed(2);
  } else {
    // Handle the calculation logic here
    insertNode.difference = curr.cases;
    insertNode.diffPercentage = insertNode.difference * 100;
  }
  acc.push(insertNode);
  return acc;
}, []);
console.log(result);

edited Aug 11, 2021 at 10:41

answered Aug 11, 2021 at 4:54

Nitheesh

20.1k3 gold badges28 silver badges52 bronze badges

7 Comments

Vadivel A Over a year ago

Thank you so much Nitheesh, for your code and explanation. Now, I got it and code works fine as expected.

Nitheesh Over a year ago

@VadivelA You are welcome. Please approve this answer if this is what you are looking for. Happy to have an upvote aswell.

Vadivel A Over a year ago

Hi Nitheesh, One strange behaviour also needs to handle here. if var day1 = [{id: 1, type:"20H", cases: 30, fail: 5}, {id: 1, type:"12C", cases: 10, fail: 3}, {id: 1, type:"4B", cases: 20, fail: 8}, {id: 1, type:"49B", cases: 20, fail: 8}]; have additionally one entry with type 49B, those entry also want to add in result array.

Nitheesh Over a year ago

@VadivelA this can be handled by checking whether there is a matching node in day5 array. I have handled this in my Array.reduce solution.

Nitheesh Over a year ago

@VadivelA Please approve this answer then. Happy to have an upvote aswell.

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