How to add a new entry to an array after a certain property changes?-CodePudding

I am trying to add a new entry to an array after a certain property, in my case " place", changes. However, I have big problems to find a suitable approach, because the operation depends on the next object in the array.

const initalData = [
  { storyID: 1, place: 12, type: "Story" },
  { storyID: 5, place: 12, type: "Story" },
  { storyID: 99, place: 45, type: "Story" }, 
  { storyID: 8, place: 31, type: "Story" },
  { storyID: 16, place: 31, type: "Story" },
  { storyID: 20, place: 45, type: "Story" },
  { storyID: 22, place: 45, type: "Story" },
];

const targetData = [
  { placeID: 12, type: "Place" }, // new added entry based on the next  "place"
  { storyID: 1, place: 12, type: "Story" },
  { storyID: 5, place: 12, type: "Story" },
  { placeID: 45, type: "Place" }, // // new added entry based on the next  "place"
  { storyID: 99, place: 45, type: "Story" },
  { placeID: 31, type: "Place" }, // new added entry based on the next  "place"
  { storyID: 8, place: 31, type: "Story" },
  { storyID: 16, place: 31, type: "Story" },
  { placeID: 45, type: "Place" },// new added entry based on the next  "place"
  { storyID: 20, place: 45, type: "Story" },
  { storyID: 22, place: 45, type: "Story" },
];

Currently I have looked at groupBy("place") as a possible approach, but the ultimate array structure here is not what I need.

CodePudding user response：

Here is the implementation

const initalData = [
    { storyID: 1, place: 12, type: "Story" },
    { storyID: 5, place: 12, type: "Story" },
    { storyID: 99, place: 45, type: "Story" },
    { storyID: 8, place: 31, type: "Story" },
    { storyID: 16, place: 31, type: "Story" },
    { storyID: 20, place: 45, type: "Story" },
    { storyID: 22, place: 45, type: "Story" },
];

let oldPlace = null;
let resultData = [];

for (let row of initalData) {
    if (row.place != oldPlace) {
        resultData.push({ placeID: row.place, type: "Place" });
        oldPlace = row.place;
    }
    resultData.push(row);
}

console.log (resultData);