Lodash _.countBy() Method

Syntax, Parameter and Return Value

Syntax: 

_.countBy(collection, [iteratee=_.identity])

Parameters:

• collection (Array|Object): The collection to iterate over.
   
• [iteratee=_.identity] (Function): The iteratee to transform keys.

Return Value: 

(Object) - Returns the composed aggregate object.

Examples 

Counting Numbers by Even and Odd:

• JavaScript

JavaScript

var _ = require('lodash');

var numbers = [1, 2, 3, 4, 5, 6];

var countByEvenOdd = _.countBy(numbers, num => num % 2 === 0 ? 'even' : 'odd');

console.log(countByEvenOdd); 

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Output:

{ 'odd': 3, 'even': 3 }

This example demonstrates counting numbers based on whether they are even or odd.

Categorizing Strings by Length:

• JavaScript

JavaScript

var words = ['sky', 'wood', 'forest', 'cliff', 'castle', 'river'];

var countByLength = _.countBy(words, 'length');

console.log(countByLength); 

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 Output: 

{ '3': 2, '5': 2, '6': 2 }

Here, strings are categorized and counted based on their length.

Counting Objects by Property:

• JavaScript

JavaScript

var objects = [{ 'type': 'fruit', 'name': 'apple' }, 

               { 'type': 'vegetable', 'name': 'carrot' },

               { 'type': 'fruit', 'name': 'banana' }];

var countByType = _.countBy(objects, 'type');

console.log(countByType); 

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Output: 

{ 'fruit': 2, 'vegetable': 1 }

An example showing how to count objects based on a shared property.

Counting with Custom Function:

• JavaScript

JavaScript

var items = [1.3, 2.1, 2.4];

var countByIntegerPart = _.countBy(items, Math.floor);

console.log(countByIntegerPart); 

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Output: 

{ '1': 1, '2': 2 }

Demonstrates using a custom function to determine the counting criterion.

Frequently Asked Questions 

Can _.countBy() handle mixed data types in a collection?

Yes, it can categorize and count mixed data types, provided the iteratee function can handle them appropriately.

How does _.countBy() differ from _.groupBy()?

While _.groupBy() groups elements without counting, _.countBy() categorizes elements and provides a count for each category.

Is _.countBy() efficient for large collections?

_.countBy() is generally efficient for large collections, but its performance may vary depending on the complexity of the iteratee function.

Conclusion

Lodash's _.countBy() method is a powerful and flexible tool for categorizing and counting elements in a collection based on specific criteria. It aids in data analysis and manipulation by providing insights into the distribution and frequency of data elements. This method exemplifies the utility of Lodash in simplifying and enhancing data handling in JavaScript.

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