Create a array based on Map

Question

I have one map. Checking consecutive keys values on the map, I need to segregate keys & insert into a new array.

let map = new Map<string, string>();
map.set("SUNDAY", "1");
map.set("MONDAY", "2");
map.set("TUESDAY", "2");
map.set("WEDNESDAY", "4");
map.set("THURSDAY", "5");
map.set("FRIDAY", "5");
map.set("SATURDAY", "9");

Expected Output should be like this:

[{
      day: "SUNDAY",
      value: "1"
    },
    {
      day: "MONDAY-TUESDAY",
      value: "2"
    },
    {
      day: "WEDNESDAY",
      value: "4"
    },
    {
      day: "THURSDAY-FRIDAY",
      value: "5"
    },
    {
      day: "SATURDAY",
      value: "9"
    }
  ];

Answer 1

You could reduce the entries of the Map and group them based on the value . If the current value is already present in the accumulator, append a - and the current day to the object. Else, add a new key to the accumulator. Then use Object.values() to return the values of the accumulator as an array

 const map = new Map([["SUNDAY","1"],["MONDAY","2"],["TUESDAY","2"],["WEDNESDAY","4"],["THURSDAY","5"],["FRIDAY","5"],["SATURDAY","5"]]); const merged = [...map].reduce((acc, [day, value]) => { if(acc[value]) acc[value].day += `-${day}` else acc[value] = { day, value }; return acc }, {}); const output = Object.values(merged); console.log(output)

Update:

If typescript doesn't allow you to spread the Map inside an array, you can set downlevelIteration to true in tsconfig ( TypeScript and Iterator: Type 'IterableIterator' is not an array type )

You could also use Map#forEach to do the same thing. Also, if you want the day to be a range of days, you could use another variable called 'previousValue'. If the previousValue is same as current value, split the day which already exists at - and take the first value. Then append the current day

 let map = new Map([["SUNDAY","1"],["MONDAY","2"],["TUESDAY","2"],["WEDNESDAY","4"],["THURSDAY","5"],["FRIDAY","5"],["SATURDAY","5"]]); let merged = {}, previousValue; map.forEach((value, day) => { if(previousValue === value) merged[value].day = `${merged[value].day.split('-')[0]}-${day}` else merged[value] = { day, value }; previousValue = value; }) const output = Object.values(merged) console.log(output)