How to filter a Map based on a condition in Typescript?

In TypeScript, you can filter a Map based on a condition using the Map’s built-in methods along with some of JavaScript’s array methods. Since Map is iterable, you can convert it to an array, apply the filter, and then convert it back to a Map. Here’s how you can do it:

Example: Filtering a Map

Suppose you have a Map where the keys are strings and the values are numbers, and you want to filter out entries where the value is less than 50.

Here’s a step-by-step approach:

1. Create the Map:

   const myMap = new Map<string, number>([
     ['a', 10],
     ['b', 60],
     ['c', 40],
     ['d', 90]
   ]);
   

2. Convert Map to an Array: Convert the Map to an array of entries using Array.from() or the spread operator [...].

   const entriesArray = Array.from(myMap.entries());
   // or
   // const entriesArray = [...myMap.entries()];
   

3. Filter the Array: Use the filter method to filter the entries based on your condition.

   const filteredEntries = entriesArray.filter(([key, value]) => value >= 50);
   

4. Convert the Filtered Array back to a Map: Convert the filtered array back to a Map.

   const filteredMap = new Map<string, number>(filteredEntries);
   

5. Putting It All Together:

   const myMap = new Map<string, number>([
     ['a', 10],
     ['b', 60],
     ['c', 40],
     ['d', 90]
   ]);
   
   // Convert Map to Array of entries
   const entriesArray = Array.from(myMap.entries());
   
   // Filter the array based on a condition
   const filteredEntries = entriesArray.filter(([key, value]) => value >= 50);
   
   // Convert the filtered entries back to a Map
   const filteredMap = new Map<string, number>(filteredEntries);
   
   console.log(filteredMap); // Map { 'b' => 60, 'd' => 90 }
   

Summary

• Convert the Map to an array of its entries.
• Use array methods like filter to apply your condition.
• Convert the filtered array back to a Map.

This approach ensures that you can efficiently filter Map entries based on your conditions while taking advantage of TypeScript’s type safety.