How to set multiple values at single key in JavaScript

Question

I am trying to group the data according to expiry.

Here is the input object:

obj = [{strikePrice: 0, expiry: 20220218},
    {strikePrice: 1, expiry: 20220218},
    {strikePrice: 2, expiry: 20220218},
    {strikePrice: 3, expiry: 20220218},
    {strikePrice: 4, expiry: 20220218},
    {strikePrice: 5, expiry: 20220219},
    {strikePrice: 6, expiry: 20220219},
    {strikePrice: 7, expiry: 20220219},
    {strikePrice: 8, expiry: 20220219},
    {strikePrice: 10, expiry: 20220220},
    {strikePrice: 11, expiry: 20220220},
    {strikePrice: 12, expiry: 20220220},
    {strikePrice: 13, expiry: 20220220},
    {strikePrice: 14, expiry: 20220221},
    {strikePrice: 15, expiry: 20220221},
    {strikePrice: 16, expiry: 20220221},
    {strikePrice: 17, expiry: 20220221},];

Expected output:

output: [{expiry: 20220218, strikePrice:[1,2,3,4 ]},
    {expiry: 20220219, strikePrice:[5,6,7,8 ]},
    {expiry: 20220220, strikePrice:[10,11,12,13 ]},
    {expiry: 20220221, strikePrice:[14,15,16,17 ]},
    ]

I am trying to solve this by using the following method:

function setValue(map, key, value) {
    if (!map.has(key)) {
        map.set(key, new Set(value));
        return;
    }
    map.get(key).add(value);

}
var myMap = new Map();
for (let i = 0; i < obj.length; i++) {
    setValue(myMap, obj[i].strikePrice, obj[i].expiry);
}
console.log(Array.from(myMap.entries(), ([k, v]) => [k, [...v]]));

but I am getting this error

    node /tmp/Gj6NKhzMbI.js
/tmp/Gj6NKhzMbI.js:21
        map.set(key, new Set(value));
                     ^

TypeError: 20220218 is not iterable
    at new Set (<anonymous>)
    at setValue (/tmp/Gj6NKhzMbI.js:21:22)
    at Object.<anonymous> (/tmp/Gj6NKhzMbI.js:29:5)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:831:12)
    at startup (internal/bootstrap/node.js:283:19)

Please give me some valuable suggestions.

Answer 1

here is my suggestion , by using FindIndex

let obj = [{strikePrice: 0, expiry: 20220218},
    {strikePrice: 1, expiry: 20220218},
    {strikePrice: 2, expiry: 20220218},
    {strikePrice: 3, expiry: 20220218},
    {strikePrice: 4, expiry: 20220218},
    {strikePrice: 5, expiry: 20220219},
    {strikePrice: 6, expiry: 20220219},
    {strikePrice: 7, expiry: 20220219},
    {strikePrice: 8, expiry: 20220219},
    {strikePrice: 10, expiry: 20220220},
    {strikePrice: 11, expiry: 20220220},
    {strikePrice: 12, expiry: 20220220},
    {strikePrice: 13, expiry: 20220220},
    {strikePrice: 14, expiry: 20220221},
    {strikePrice: 15, expiry: 20220221},
    {strikePrice: 16, expiry: 20220221},
    {strikePrice: 17, expiry: 20220221},];
let result = []

obj.map(y => {
  let index = result.findIndex(x => x.expiry == y.expiry)
  if(index == -1) {
    result.push({ expiry: y.expiry, strikePrice: [y.strikePrice]})
  } else {
    result[index].strikePrice.push(y.strikePrice)
  }
})

console.log(result)

Answer 2

A single reduce iteration already does the job of grouping and collecting/merging.

But in order to let everything happen within a single run, one needs to utilize the initial value as config/tracking reference where one does both, keeping track (indexing) of the new single expiry specific group item and storing it within the final result array ...

console.log([

  { strikePrice: 0, expiry: 20220218 },
  { strikePrice: 1, expiry: 20220218 },
  { strikePrice: 2, expiry: 20220218 },
  { strikePrice: 3, expiry: 20220218 },
  { strikePrice: 4, expiry: 20220218 },
  { strikePrice: 5, expiry: 20220219 },
  { strikePrice: 6, expiry: 20220219 },
  { strikePrice: 7, expiry: 20220219 },
  { strikePrice: 8, expiry: 20220219 },
  { strikePrice: 10, expiry: 20220220 },
  { strikePrice: 11, expiry: 20220220 },
  { strikePrice: 12, expiry: 20220220 },
  { strikePrice: 13, expiry: 20220220 },
  { strikePrice: 14, expiry: 20220221 },
  { strikePrice: 15, expiry: 20220221 },
  { strikePrice: 16, expiry: 20220221 },
  { strikePrice: 17, expiry: 20220221 },

].reduce(({ index, result }, item) => {
  const groupKey = item.expiry;
  let groupItem = index[groupKey];

  if (!groupItem) {
    groupItem = index[groupKey] = {
      expiry: groupKey,
      strikePrice: [],
    };
    result.push(groupItem);
  }
  groupItem.strikePrice.push(item.strikePrice);

  return { index, result };

}, { index: {}, result: [] }).result);

.as-console-wrapper { min-height: 100%!important; top: 0; }

One of cause could achieve the same with a simpler/more common reduce tasks which reduces/merges the original data into an expiry key based object.

In order to then still meet the OP's requirements of an array-based end-result one additionally and finally has to pass the reduced object through Object.values

console.log(
  Object.values([

    { strikePrice: 0, expiry: 20220218 },
    { strikePrice: 1, expiry: 20220218 },
    { strikePrice: 2, expiry: 20220218 },
    { strikePrice: 3, expiry: 20220218 },
    { strikePrice: 4, expiry: 20220218 },
    { strikePrice: 5, expiry: 20220219 },
    { strikePrice: 6, expiry: 20220219 },
    { strikePrice: 7, expiry: 20220219 },
    { strikePrice: 8, expiry: 20220219 },
    { strikePrice: 10, expiry: 20220220 },
    { strikePrice: 11, expiry: 20220220 },
    { strikePrice: 12, expiry: 20220220 },
    { strikePrice: 13, expiry: 20220220 },
    { strikePrice: 14, expiry: 20220221 },
    { strikePrice: 15, expiry: 20220221 },
    { strikePrice: 16, expiry: 20220221 },
    { strikePrice: 17, expiry: 20220221 },

  ].reduce((index, item) => {

    const groupItem = index[item.expiry] ??= {
      expiry: item.expiry,
      strikePrice: [],
    };
    groupItem.strikePrice.push(item.strikePrice);

    return index;

  }, {}))
);

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