How to convert an array to a dictionary in Typescript?

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Do you want to convert an array to a dictionary in Typescript? In this Typescript tutorial, I have explained how to convert an array to a dictionary in Typescript using various methods.

Convert an array to a dictionary in Typescript

Here, we will discuss a few methods to convert an array to a dictionary in Typescript.

1. Using the Array reduce() Function

The reduce() method is a versatile tool in TypeScript for accumulating values. Here’s how you can use it to convert an array to a dictionary in Typescript.

Here is the complete code:

interface Dictionary<T> {
  [key: string]: T;
}

function arrayToDictionary<T>(array: T[], keyField: keyof T): Dictionary<T> {
  return array.reduce((obj, item) => {
    obj[item[keyField]] = item;
    return obj;
  }, {} as Dictionary<T>);
}

// Example usage:
interface User {
  id: string;
  name: string;
}

const users: User[] = [
  { id: 'user1', name: 'John Doe' },
  { id: 'user2', name: 'Jane Doe' }
];

const userDictionary = arrayToDictionary(users, 'id');
console.log(userDictionary);

2. Using the for…of Loop

The Typescript for…of loop offers a straightforward way to create a dictionary from an array. Here is the complete code:

interface Dictionary<T> {
    [key: string]: T;
  }
  
  function arrayToDictLoop<T>(array: T[], keyField: keyof T): Dictionary<T> {
    const dictionary: Dictionary<T> = {};
    for (const item of array) {
      dictionary[item[keyField] as any] = item;
    }
    return dictionary;
  }
  
  // Example usage:
  interface User {
    id: string;
    name: string;
  }
  
  const users: User[] = [
    { id: 'user1', name: 'John Doe' },
    { id: 'user2', name: 'Jane Doe' }
  ];
  
  const userDictLoop = arrayToDictLoop(users, 'id');
  console.log(userDictLoop);

Output:

{
  user1: { id: 'user1', name: 'John Doe' },
  user2: { id: 'user2', name: 'Jane Doe' }
}

In this snippet, the arrayToDictLoop function is iterating over each element of the array using the for…of loop and adding each item to a new dictionary object based on the specified key field.

You can see the output in the screenshot below.

convert array to dictionary typescript

3. Using Array forEach() Method

TypeScript’s forEach() method on arrays is another way to iterate through elements and perform operations:

interface Dictionary<T> {
  [key: string]: T;
}

function arrayToDictForEach<T extends Record<K, PropertyKey>, K extends keyof T>(
  array: T[],
  keyField: K
): Dictionary<T> {
  const dictionary: Dictionary<T> = {};
  array.forEach((item) => {
    dictionary[item[keyField]] = item;
  });
  return dictionary;
}

// Example usage with a User interface:
interface User {
  id: string;
  name: string;
}

const users: User[] = [
  { id: 'user1', name: 'John Doe' },
  { id: 'user2', name: 'Jane Doe' }
];

const userDictForEach = arrayToDictForEach(users, 'id');
console.log(userDictForEach);

Conclusion

In this Typescript tutorial, I have explained how to convert an array to a dictionary in Typescript using reduce(), for…of loops, and forEach() methods.

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