Dictionary to array typescript

JavaScript: Map an array of objects to a dictionary

Hey!! can you explain please why did you use the Rest parameter syntax with . data?

it’s because data is an array, so its map is also an array, and when you use . data — it spreads the array elements to be function parameters, which get to be one-prop objects, with which the resulting object is updated. Beautiful!

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How To Build A Dictionary In TypeScript?

The dictionary, also called map or associative array, is one of the fundamental data structures in computer science. But what is it, and how to build one in TypeScript?

In TypeScript, you can build a dictionary using:

This article explains the different methods of building a dictionary with clear code examples.

What is a dictionary?

A dictionary is an unordered collection of key/value pairs.

This data structure must follow those simple rules:

Generally, a dictionary’s key is of type string , but it also can be of type number .

On the other hand, each key’s value can be of any type you want.

Way #1 — Using an indexed interface

The easiest way to build a dictionary is to create an annotated indexed interface AND use it on an empty object. Here is an example:

typescriptinterface IDictionary < Dictionary to array typescript: string; > const dictionary: IDictionary = <>; dictionary['key1'] = 'value1'; dictionary['key2'] = 'value2'; // To verify if a key exists. // Outputs: true console.log('key1' in dictionary); // To get a key's value. // Outputs: 'value1' console.log(dictionary['key1']); 

As you can see, in this example, we create a simple dictionary AND add key/value pairs. You can also create a generic indexed interface if you want to reuse the dictionary interface with different value types. Here is an example:

typescriptinterface IDictionary < Dictionary to array typescript: T; > const dictionary: IDictionarystring> = <>; dictionary['key1'] = 'value1'; const dictionary2: IDictionarynumber> = <>; dictionary2['key1'] = 1; 

In this example, the first dictionary can only contain string values, and the second can only have number values.

Way #2 — Using the Record utility type

Another option to build a dictionary in TypeScript involves using the Record utility type. Here is an example:

typescriptconst dictionary: Recordstring, string> = <>; dictionary['key1'] = 'value1'; dictionary['key2'] = 'value2'; 

This method is similar to the indexed interface but easier since you don’t have to create a new interface.

Way #3 — Using the ES6 built-in Map object

typescriptconst dictionary = new Mapstring, string>(); dictionary.set('key1', 'value1'); dictionary.set('key2', 'value2'); // To verify if a key exists. // Outputs: true console.log(dictionary.has('key1')); // To get a key's value. // Outputs: 'value1' console.log(dictionary.get('key1')); 

Compared to other methods, the main advantage of using the Map object is its API methods to manage key/value pairs.

Final thoughts

As you can see, building a dictionary is simple in TypeScript. In my day-to-day programming life, I prefer to create dictionaries using the ES6 built-in Map object. This method is the simplest to understand for new programmers and easy to refactor. A polyfill

exists if you want to use the ES6 Map object in older browsers. Here are some other TypeScript tutorials for you to enjoy:

• Check for undefined in TypeScript
• TypeScript tuples

The best Web Development course in 2023! 👉 Learn Web Development

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Typescript Dictionary Complete Guide with examples

In this Blog Post, Learn the dictionary in typescript with examples.

Dictionary is a type of data structure with unordered list data, that contains key and value values. It is the same as map type in typescript.

Does TypeScript have dictionary?

Typesript has no dictionary name type, however it has Map that stores list of key and values. And data is unordered key and values. Es6 introduced Map type and created Map object using types in Typescript. You can create a dictionary using map as given below Using new and Map keyword with key and value types are declared. valid key and value types are string,number,boolean and class or interface objects.

let dictionary = new Mapstring, string>();

How to declare and initialize a dictionary in a Typescript?

dictionary can be created using map keyword in typescript.

A map is a type introduced in ES6, It adds type safety to key and values in typescript.

the declare and create a map variable using new operator and key and value types are declared

let employees = new Mapstring, string>();

add the key-value pairs to an map using set method.

// Checking for the key exist : employees.has("name"); // true

// get a value by a key: employees.get("name"); // john

// delete an item by a key: employees.delete("name");

// iterate key and values employees.forEach((item, key) => console.log(item));

// remove all from map: employees.clear();

// size:Number of elements in Map : console.log(employees.size);

// get All keys with insertion order let keys = Array.from(employees.keys()); // Extract values with insertion order let values = Array.from(employees.values());

Here is an complete example

let employees = new Mapstring, string>(); employees.set("name", "john"); // Checking for the key exist : employees.has("name"); // true // get a value by a key: employees.get("name"); // john // delete an item by a key: employees.delete("name"); // iterate key and values employees.forEach((item, key) => console.log(item)); // remove all from map: employees.clear(); // size:Number of elements in Map : console.log(employees.size); // get All keys with insertion order let keys = Array.from(employees.keys()); // Extract values with insertion order let values = Array.from(employees.values());

How to get key values from a dictionary in TypeScript?

employees.forEach((item, key) => console.log(key));

How to iterate through keys in TypeScript Dictionary?

Multiple ways to return the keys of an map in Typescript One way using

How to declare an interface for a dictionary in typescript?

Declare an interface using indexable type in typescript

declare an interface that accepts a key as a string and value of type T

interface DictionaryT>  [Key: string]: T; >

A class contains properties of the dictionary interface as below.

export class AllEmployees  employees: Dictionarystring> = <>; >

Dictionary interfaces declare with let keyword and initialize the values, add the values.

let emps: Dictionarystring> = <>; emps["name"] = "john";

How to declare a dictionary with record type in typescript

Record is a map of key and value pairs.

A new type creates with a type alias(type keyword) and Record type.

type emps = Recordstring, string>;

Data initialized using object syntax as seen below.

let emps: Recordstring, string> =  "name": "john" >, "id": "1" > >;

Conclusion

Learned typescript dictionaries with multiple examples to declare a dictionary type in typescript

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Dictionary to array typescript

initalize the Dictionary, iterate over dictionary, check if particular key is already present, add an element in dictionary, get the length of the dictionary, delete an element from dictionary, get key array from dictionary, get value array from dictionary.

import * as React from 'react'; export default class App extends React.Component  < public render() < this.useDictionary(); return ( 
Learn Dictionary
 ); > private useDictionary(): void < //initalize the Dictionary const studentDictionary: _.Dictionary= < ["11"]: "ram", ["12"]: "sam" >; //iterate over dictionary for (const key of Object.keys(studentDictionary)) < console.log("key is " + key); console.log("value is " + studentDictionaryDictionary to array typescript); >//add an element in dictionary studentDictionary["13"] = "raj"; //check if particular key is already present if (studentDictionary["13"]) < console.log("13 is present"); >else < console.log("13 is not present"); >//delete an element from dictionary delete studentDictionary["11"]; //get the length of the dictionary console.log("Length of the dictionary is " + Object.keys(studentDictionary).length); //get key array from dictionary const keyArray = Object.keys(studentDictionary); console.log(keyArray); //get value array from dictionary const valueArray = Object.keys(studentDictionary).map(key => studentDictionaryDictionary to array typescript); console.log(valueArray); > >

key is 11
App.tsx:25 value is ram
App.tsx:24 key is 12
App.tsx:25 value is sam
App.tsx:33 13 is present
App.tsx:42 Length of the dictionary is 2
App.tsx:46 Array(2) 0: “12”1: “13”
App.tsx:50 Array(2) 0: “sam”1: “raj”

Package.json

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