regex remove duplicates

Regex Remove Duplicates

Have you ever encountered situations where you need to remove duplicate values from a large dataset? This can be a tedious and time-consuming process if done manually. Luckily, regular expressions or regex can help solve this problem quickly and efficiently.

Regex Syntax

Regular expressions are a sequence of characters that define a search pattern. They are used to match and manipulate text based on a specific pattern. In the case of removing duplicates, we can use the regex syntax to search for repeated patterns and replace them with a single instance.

The syntax for regular expressions varies slightly depending on the programming language being used. However, most languages support the basic regex syntax. Some common regex characters include:

  • * - Matches zero or more characters
  • + - Matches one or more characters
  • ? - Matches zero or one character
  • . - Matches any character except newline
  • | - Matches either the left or right expression
  • () - Groups expressions together
  • [] - Matches any character within the brackets

Removing Duplicates with Regex

To remove duplicates using regex, we need to identify the pattern that is repeating and replace it with a single instance. For example, if we have a list of names that contain duplicates, we can use regex to remove them.

var names = ["John", "Jane", "John", "Alex", "Jane"];

var uniqueNames = names.filter(function(item, pos) {
    return names.indexOf(item) == pos;


In the above example, we have an array of names that contain duplicates. We can use the filter function to remove duplicates and return an array of unique names. The filter function takes a callback function as an argument that performs the actual filtering. The callback function checks if the current item is equal to its index in the array. If it is, it means it is the first occurrence of that item, and it is added to the new array of unique names.

Another way to remove duplicates using regex is to use the string replace function. The replace function takes two arguments, the pattern to search for and the replacement string. We can use regex to search for the repeating pattern and replace it with a single instance.

var names = "John, Jane, John, Alex, Jane";

var uniqueNames = names.replace(/(\b\w+\b)(?=.*\b\1\b)/g, "");


In this example, we have a string of names separated by commas. We use regex to search for repeating words and replace them with an empty string. The regex pattern searches for a word boundary, followed by one or more word characters, followed by a positive lookahead for the same word boundary and word characters. This matches any repeated words and replaces them with an empty string.


Removing duplicates from a dataset can be a daunting task if done manually. However, with the power of regular expressions, we can quickly and efficiently remove duplicates using a few lines of code.

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