How to create an array of partial objects from another array in JavaScript ?
Creating an array of partial objects from another array is a useful technique in JavaScript, especially for data transformation and manipulation. This guide covers various methods to efficiently create these arrays, enhancing your ability to work with complex data structures.
Importance of Creating Partial Objects:
Creating partial objects is crucial for:
- Simplifying data structures for specific use cases.
- Improving performance by reducing the size of data handled.
- Enhancing readability and maintainability of code by focusing on relevant properties.
These are some common methods:
Table of Content
- Using the map() method
- Using Destructuring
- Using reduce Method()
- Using forEach() method
- Using a for Loop
1. Using the map() method
By using the map() method we can create an array of partial objects from another object’s array. The map() method takes the keys of the object array as the parameters which are required to be in the desired object array and returns the key-value pairs of that particular key. In the below example, we obtain the key-value pairs of the name and age as the array of partial objects of which the parameters are given in the map method.
Syntax:
partialObjectArray = ObjectArray.map((
{key 1, key 2, ...key n}) => ({key 1, key 2, ...key n}));
Note: key 1, key 2, …key n are the fields that are needed in the partial object array
Example: This is the illustration of creating an array of partial objects from another array using the map() method.
let = studentDetails = [
{
name: 'dinesh',
age: 20,
marks: 30,
Grade: 'F'
},
{
name: 'divi',
age: 20,
marks: 60,
Grade: 'B'
},
{
name: 'vignesh',
age: 30,
marks: 80,
Grade: 'A'
}]
let partialStudentDetails = studentDetails.map((
{ name, age, Grade }) => ({ name, age, Grade }));
console.log(partialStudentDetails);
Output
[
{ name: 'dinesh', age: 20, Grade: 'F' },
{ name: 'divi', age: 20, Grade: 'B' },
{ name: 'vignesh', age: 30, Grade: 'A' }
]
2. Using Destructuring
Rather than giving all the required fields of the object array in the map() method which is a difficult task if there are multiple fields in the object. we can use the map method in the below way to create a partial object array. The first parameters must be the fields that are not needed in the resultant object array.
Syntax:
partialObjectArray = ObjectArray.map(({ key 1, key 2, ...rest }) => rest);
Note: key 1, and key 2 are the fields that are not required in the resultant object array.
Example: This is another illustration to create an array of partial objects from another array using the map() method.
let = studentDetails = [
{
name: 'dinesh',
age: 20,
marks: 30,
Grade: 'F'
},
{
name: 'divi',
age: 20,
marks: 60,
Grade: 'B'
},
{
name: 'vignesh',
age: 30,
marks: 80,
Grade: 'A'
}]
// The parameter marks is not required
// in the resultant object array
let partialStudentDetails = studentDetails.map((
{ marks, ...rest }) => rest);
console.log(partialStudentDetails);
Output
[
{ name: 'dinesh', age: 20, Grade: 'F' },
{ name: 'divi', age: 20, Grade: 'B' },
{ name: 'vignesh', age: 30, Grade: 'A' }
]
In the above example, we get name, age, and marks key-value pairs in a partial object array.
3. Using reduce Method()
Reduce method also use to iterate over an array and create a single value and object,
Example: In this example, we are using reduce method to create a partial object from another array.
let studentDetails = [
{
name: 'dinesh',
age: 20,
marks: 30,
},
{
name: 'divi',
age: 20,
marks: 60,
},
{
name: 'vignesh',
age: 30,
marks: 80,
}]
const partialStudentDetails = studentDetails.reduce((res, item) => {
res.push({ name: item.name, age: item.age, marks: item.marks });
return res;
}, []);
console.log(partialStudentDetails);
Output
[
{ name: 'dinesh', age: 20, marks: 30 },
{ name: 'divi', age: 20, marks: 60 },
{ name: 'vignesh', age: 30, marks: 80 }
]
4. Using forEach() method
The arr.forEach() method calls the provided function once for each element of the array. The provided function may perform any kind of operation on the elements of the given array.
Syntax:
array.forEach(callback(element, index, arr), thisValue);
Example: In this example, the forEach() method is used to iterate over each object in the originalArray. For each object, a new partial object is created with selected properties (in this case, id and name), and it is pushed to the partialObjectsArray.
// Original array of objects
const originalArray = [
{ id: 1, name: 'John', age: 30 },
{ id: 2, name: 'Alice', age: 25 },
{ id: 3, name: 'Bob', age: 35 },
];
// Array to store partial objects
const partialObjectsArray = [];
// Using forEach() to create partial objects
originalArray.forEach(obj => {
const partialObj = {};
partialObj.id = obj.id;
partialObj.name = obj.name;
// You can include other properties as needed
partialObjectsArray.push(partialObj);
});
console.log(partialObjectsArray);
Output
[
{ id: 1, name: 'John' },
{ id: 2, name: 'Alice' },
{ id: 3, name: 'Bob' }
]
5. Using a for Loop
To create an array of partial objects using a for loop, iterate over the original array, destructure the desired properties, and push new objects containing these properties into a result array. This method extracts and collects specific fields efficiently.
Example:
let studentDetails = [
{
name: 'dinesh',
age: 20,
marks: 30,
},
{
name: 'divi',
age: 20,
marks: 60,
},
{
name: 'vignesh',
age: 30,
marks: 80,
}
];
const partialStudentDetails = [];
for (const student of studentDetails) {
partialStudentDetails.push({
name: student.name,
age: student.age,
marks: student.marks
});
}
console.log(partialStudentDetails);
Output
[
{ name: 'dinesh', age: 20, marks: 30 },
{ name: 'divi', age: 20, marks: 60 },
{ name: 'vignesh', age: 30, marks: 80 }
]
Mastering the creation of partial objects from arrays is a valuable skill in JavaScript programming. This guide introduces the importance and prerequisites, setting the stage for detailed method explanations. By focusing on practical applications, you can improve your data handling and code efficiency.
Contact Us