angularjs filter array with code examples

AngularJS is a powerful JavaScript framework used for developing dynamic single-page applications. One of the powerful features of AngularJS is its ability to filter an array of data quickly and easily. In this article, we will explore how to filter an array in AngularJS with code examples.

Filtering an array involves performing operations on an array to extract a subset of elements that meet certain criteria. AngularJS provides a filter service that can be used to filter an array by creating a new filtered array that matches the specified criteria. The filter service can take various arguments to perform filtering operations, such as the filter expression and the comparator function.

Filter Expression

The filter expression is a string that is used to specify the criteria for filtering an array. The filter expression can be a simple string or a complex expression that involves multiple conditions. The syntax for the filter expression is as follows:

{{ expression | filter : options }}

Here, the expression is the data object that is to be filtered, and the filter is the name of the filter service. The options parameter is optional and can be used to pass additional options to the filter service.

Let's look at some examples of how to filter an array using the filter expression.

Example 1:

Suppose we have an array of numbers:

var numbers = [2, 4, 6, 8, 10];

We want to filter this array to extract only the even numbers. We can use the filter expression as follows:

<ul>
	<li ng-repeat="n in numbers | filter : 'even'">{{ n }}</li>
</ul>

Here, the 'even' string specifies the condition for filtering the array. The output of this code will be:

2
4
6
8
10

Example 2:

Suppose we have an array of objects that contain the name and age of people:

var people = [
	{name: 'John', age: 25},
	{name: 'Sarah', age: 30},
	{name: 'Peter', age: 35},
	{name: 'Emma', age: 40}
];

We want to filter this array to extract only the people whose age is greater than or equal to 35. We can use the filter expression as follows:

<ul>
	<li ng-repeat="person in people | filter : { age: '>=35' }">{{ person.name }}</li>
</ul>

Here, the filter object specifies the condition for filtering the array. The key 'age' is used to specify the field in the object that we want to filter. The value '>=35' is the condition for the filter.

The output of this code will be:

Peter
Emma

Comparator Function

The comparator function is used to define a custom comparison function that can be used to sort the array according to a specific condition. The comparator function takes two arguments, which are the current and next values in the array. The function should return -1, 0, or 1, depending on how the values compare with each other.

Let's look at some examples of how to use the comparator function to filter an array.

Example 1:

Suppose we have an array of numbers:

var numbers = [2, 4, 6, 8, 10];

We want to filter this array to extract only the numbers less than or equal to 6, but in descending order. We can use the comparator function as follows:

<ul>
	<li ng-repeat="n in numbers | filter : customFilter">{{ n }}</li>
</ul>
$scope.customFilter = function (value, index, array) {
  return value <= 6 ? 1 : -1;
};

Here, the customFilter function specifies the condition for filtering the array. The function returns 1 if the value is less than or equal to 6, which means that the value should be included in the filtered result. If the value is greater than 6, the function returns -1, which means that the value should not be included in the filtered result.

The output of this code will be:

6
4
2

Example 2:

Suppose we have an array of objects that contain the name and age of people:

var people = [
	{name: 'John', age: 25},
	{name: 'Sarah', age: 30},
	{name: 'Peter', age: 35},
	{name: 'Emma', age: 40}
];

We want to filter this array to extract only the people whose name contains the string 'a' and sort them in descending order of age. We can use the comparator function as follows:

<ul>
	<li ng-repeat="person in people | filter: { name: 'a' } : customSort">{{ person.name }} ({{ person.age }})</li>
</ul>
$scope.customSort = function (a, b) {
  return a.age > b.age ? -1 : a.age < b.age ? 1 : 0;
};

Here, the customSort function specifies the condition for sorting the array. The function compares the age values of the two objects and returns -1, 1, or 0, depending on the comparison result.

The output of this code will be:

Emma (40)
Peter (35)
Sarah (30)

Conclusion

In this article, we have explored how to filter an array in AngularJS. We have seen how to use the filter service with filter expressions and the comparator function to filter and sort an array according to specific conditions. By using these techniques, you can easily filter and sort arrays in your AngularJS applications to extract relevant data for your needs.

let's dive deeper into the filter expression and comparator function that we mentioned before.

Filter Expression

The filter expression in AngularJS is a powerful tool used to perform operations on arrays to extract a subset of elements that meet certain criteria. The filter service can take various arguments to perform filtering operations, such as the filter expression and the options parameter.

The filter expression can be a simple string with a specific condition, or it can be a more complex expression with multiple conditions. Here are some examples of different filter expressions:

  • 'John': This filter expression will return all elements that contain the word 'John'
  • '!John': This filter expression will return all elements that do not contain the word 'John'
  • '35': This filter expression will return all elements that contain the value '35'
  • '<35': This filter expression will return all elements that have a value less than 35
  • '>=35': This filter expression will return all elements that have a value greater than or equal to 35

The filter expression can also be combined with the options parameter to perform more specific operations on the array. For example, we can specify the filter expression and the property to filter by, like this:

{{ expression | filter:{name:'John'} }}

This will filter the expression by the property 'name' and only show the elements that contain the value 'John'.

Comparator Function

The comparator function in AngularJS is used to define a custom comparison function that can be used to sort the array according to a specific condition. The function takes two arguments, which are the current and next values in the array. The function should return -1, 0, or 1, depending on how the values compare with each other.

Here's an example of how the comparator function can be used:

Suppose we have an array of objects with properties 'name' and 'age'. We want to sort the array in descending order of age, but if two elements have the same age, we want to sort them in ascending order of name. We can use a custom comparator function to achieve this:

$scope.customSort = function(a, b) {
    if (a.age > b.age) return -1;
    if (a.age < b.age) return 1;
    if (a.name < b.name) return -1;
    if (a.name > b.name) return 1;
    return 0;
};

In this function, we first compare the ages of the two elements. If the age of the first element is greater than that of the second, we return -1, which means that the first element should come before the second. If the age of the first element is less than that of the second, we return 1, which means that the second element should come before the first.

If the two elements have the same age, we then compare their names. If the name of the first element is less than that of the second, we return -1, and so on.

Using the filter service with a custom comparator function is easy. Here's an example of how to sort the array using the customSort function:

{{ expression | orderBy:customSort }}

In this example, we are using the orderBy filter to sort the expression using the customSort function.

Overall, the filter expression and comparator function in AngularJS provide a powerful set of tools for filtering and sorting arrays. When used together, they can help you quickly extract relevant data and sort it according to specific criteria.

Popular questions

  1. What is the filter expression in AngularJS?
    Answer: The filter expression in AngularJS is a string that is used to specify the criteria for filtering an array. The filter expression can be a simple string or a complex expression that involves multiple conditions.

  2. How can we use the filter service to filter an array?
    Answer: We can use the filter service in AngularJS by applying the filter filter to an array, followed by the specified filter expression and any additional options.

  3. How can we use the comparator function to sort an array in AngularJS?
    Answer: We can use the comparator function in AngularJS by applying the orderBy filter to an array, followed by the specified custom comparator function.

  4. What are some examples of filter expressions in AngularJS?
    Answer: Some examples of filter expressions in AngularJS include 'John', '!John', '35', '<35', and '>=35', depending on the specific needs of the filtering operation.

  5. How can we filter an array of objects in AngularJS?
    Answer: We can filter an array of objects in AngularJS by specifying the field in the object that we want to filter and the value or condition for the filter, using the filter expression and options parameter, like this: {{ expression | filter: { field: 'value' } }}.

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As an experienced software engineer, I have a strong background in the financial services industry. Throughout my career, I have honed my skills in a variety of areas, including public speaking, HTML, JavaScript, leadership, and React.js. My passion for software engineering stems from a desire to create innovative solutions that make a positive impact on the world. I hold a Bachelor of Technology in IT from Sri Ramakrishna Engineering College, which has provided me with a solid foundation in software engineering principles and practices. I am constantly seeking to expand my knowledge and stay up-to-date with the latest technologies in the field. In addition to my technical skills, I am a skilled public speaker and have a talent for presenting complex ideas in a clear and engaging manner. I believe that effective communication is essential to successful software engineering, and I strive to maintain open lines of communication with my team and clients.
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