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"
    }
  ];

The question is underspecified as it's unclear how you want to combine days. The example leaves it open whether the aggregated keys are a range (e.g., "Monday-Wednesday") or just a joined array (e.g., "Monday-Tuesday-Wednesday"). — Ingo Bürk
– Ingo Bürk, Commented Apr 14, 2019 at 13:56
@IngoBürk aggregated keys are a range (e.g., "Monday-Wednesday") — Suman
– Suman, Commented Apr 14, 2019 at 14:28

adiga · Accepted Answer · 2019-04-14 13:48:22Z

2

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)

edited Apr 14, 2019 at 13:48

answered Apr 14, 2019 at 13:05

adiga

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8 Comments

lankovova Over a year ago

You missed combining days MONDAY-TUESDAY and THURSDAY-FRIDAY

Suman Over a year ago

My angular code is giving error like: Type 'Map<string, string>' is not an array type or a string type.

adiga Over a year ago

@Suman which line exactly? If it's the [...map] line, try using [...map.entries()]`

Suman Over a year ago

Yes. I already tried with entries. Its giving error like : Type 'IterableIterator<[string, string]>' is not an array type or a string type.

adiga Over a year ago

@Suman You might have to tweak tsconfig to use this TypeScript and Iterator: Type 'IterableIterator<T>' is not an array type (I'll add an answer which doesn't involve spreading the Map)

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