Start a new ID every time the date changes in an array of objects-CodePudding

I have an array of objects that looks like the following

[
 { id: 332, tech: 'bob', Date: '2022-07-25', dateID: 0 },
 { id: 342, tech: 'bob', Date: '2022-07-25', dateID: 1 },
 { id: 344, tech: 'bob', Date: '2022-07-26', dateID: 2 },
 { id: 335, tech: 'bob', Date: '2022-07-26', dateID: 3 },
 { id: 334, tech: 'bob', Date: '2022-07-29', dateID: 4 }
]

What I am trying to do is create an array of objects, so that everyTime [i].Date changes dateId starts back at 0 and increments like the following:

[
 { id: 332, tech: 'bob', Date: '2022-07-25', dateID: 0 },
 { id: 342, tech: 'bob', Date: '2022-07-25', dateID: 1 },
 { id: 344, tech: 'bob', Date: '2022-07-26', dateID: 0 },
 { id: 335, tech: 'bob', Date: '2022-07-26', dateID: 1 },
 { id: 335, tech: 'bob', Date: '2022-07-26', dateID: 2 },
 { id: 334, tech: 'bob', Date: '2022-07-29', dateID: 0 }
]

I have tried reducing the array of objects so I had an object with the date and how many times it occurs and using a nested for loop but that didn't seem to work and I cant get it with array.map.

CodePudding user response：

let data = [
 { id: 332, tech: 'bob', Date: '2022-07-25', dateID: 0 },
 { id: 342, tech: 'bob', Date: '2022-07-25', dateID: 1 },
 { id: 344, tech: 'bob', Date: '2022-07-26', dateID: 2 },
 { id: 335, tech: 'bob', Date: '2022-07-26', dateID: 3 },
 { id: 334, tech: 'bob', Date: '2022-07-29', dateID: 4 }
]

data.forEach((el, i) => {
  el.dateID = 0
  if (el.Date == data[i - 1]?.Date) {
    el.dateID  = data[i - 1].dateID   1;
  }
});

console.log(data)

CodePudding user response：

Here's another approach. Essentially what I'm doing grabbing the previously iterated item. Then I check whether the Date of the current item does not equal the Date of the previous one. If that is the case the new dateID is set to 0. If the Date is still the same the dateID will be increased.

const data = [
  { id: 332, tech: "bob", Date: "2022-07-25", dateID: 0 },
  { id: 342, tech: "bob", Date: "2022-07-25", dateID: 1 },
  { id: 344, tech: "bob", Date: "2022-07-26", dateID: 2 },
  { id: 335, tech: "bob", Date: "2022-07-26", dateID: 3 },
  { id: 334, tech: "bob", Date: "2022-07-29", dateID: 4 },
];

const output = data.reduce((acc, curr, i) => {
  const prev = acc[i - 1];
  return [
    ...acc,
    {
      ...curr,
      dateID: prev?.Date !== curr.Date ? 0 : prev?.dateID   1,
    },
  ];
}, []);

console.log(output);

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

CodePudding user response：

const data = [
 { id: 332, tech: 'bob', Date: '2022-07-25', dateID: 0 },
 { id: 342, tech: 'bob', Date: '2022-07-25', dateID: 1 },
 { id: 344, tech: 'bob', Date: '2022-07-26', dateID: 2 },
 { id: 335, tech: 'bob', Date: '2022-07-26', dateID: 3 },
 { id: 334, tech: 'bob', Date: '2022-07-29', dateID: 4 }
]

const result = data.reduce((acc, item) => {
  // try to find if there is an item with a current Item dateID exist.
  const oldItemIndex = acc.findIndex(i => i.Date === item.Date);
  
  // if exist update the dateID with one
  if (oldItemIndex !== -1) {
    item.dateID = acc[oldItemIndex].dateID   1
    acc.push(item)
    return acc
  }
  // if not update dateID to zero.
  item.dateID = 0
  acc.push(item)
  return acc

}, [])

console.log(result)