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

question typescript
Ram Patra Published on July 20, 2024

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.

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Ram Patra Published on July 20, 2024
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