How to increase all values of a map in javascript

Question

I have this map:

var map = new Map();

map.set("10/10", 0);
map.set("10/11", 1);
map.set("10/12", 2);

     
{
   "10/10": 0,
   "10/11": 1,
   "10/12": 2,
}

And I want to add this new key/value:

"10/9": 0,

How can I increase the values of all the old map elements in 1? So I get the following map:

{
   "10/9": 0,
   "10/10": 1,
   "10/11": 2,
   "10/12": 3,
}

I am storing indices of a list in this map, for getting a fast indexing. — Conchi Bermejo, Jan 21 '21 at 05:36
Iterate over the keys of the map and set them one by one?... — user202729, Jan 21 '21 at 05:42
You do realize your example is flawed, right? The Map maintains insertion order - so "10/9' will be the last key in the list, it cannot be the first in your given scenario. — Randy Casburn, Jan 21 '21 at 05:45
`[...map.keys()].forEach(k => map.set(k, map.get(k) +1));` and then `map.set("10/9", 0);` — D. Seah, Jan 21 '21 at 05:45
What you really want to do is store the dates in a `TreeSet` and use `.subset(...).size()` to determine the rank of items on demand. You'll need to provide a custom comparator, since `"10/9"` comes *after* `"10/10"` in a string sort. Or use a different type like `LocalDate` — Matt Timmermans, Jan 21 '21 at 13:59
related: https://stackoverflow.com/questions/53584369/javascript-map-increment-value — Bergi, Jan 05 '22 at 22:03

score 2 · Accepted Answer · answered Jan 21 '21 at 05:49

You can use something like this:

var map = new Map();

map.set("10/10", 0);
map.set("10/11", 1);
map.set("10/12", 2);

function addNewItem(item, map) {
  map.forEach((value, key, map) => {
    map.set(key, value + 1);
  });
  map.set(item, 0);
  return map;
}

const newMap = addNewItem("10/9", map);

console.log(newMap);

score 1 · Answer 2 · answered Jan 21 '21 at 05:56

You can place the item at any position here based on its value and increment the value greater then or equal to assigned value.

var map = new Map();

map.set("10/10", 0);
map.set("10/11", 1);
map.set("10/12", 2);



function logMapElements(value, key, map, set_key, set_value) {
    if (set_value <= value) {
      map.set(key, value+1);
    }
    
}

function setMapElement(set_key, set_value) {
        map.forEach((key, value, map) => logMapElements(key, value, map, set_key, set_value))
    map.set(set_key, set_value);
  

  
  
}

setMapElement("10/9", 0);
console.log(map.get("10/9"));
console.log(map.get("10/10"));

How to increase all values of a map in javascript

2 Answers2