Filter by regex

👉 Overview

👀 What ?

Filter by regex, or regular expression, is a method used in programming to match a certain pattern in a string or a set of strings. A regular expression, in computing terms, is a sequence of characters that forms a search pattern. This pattern can then be used to match, locate, and manage text. The 'Filter by regex' function allows users to filter data based on a particular pattern, which can be incredibly useful in a variety of applications, such as data cleaning, data extraction, and more.

🧐 Why ?

Filtering by regex is a powerful tool in the arsenal of any programmer or data analyst. It allows for efficient and precise text manipulation, which is crucial in many tasks, such as cleaning data, extracting information, or even cyber security where it can be used for pattern recognition in data exfiltration attempts. Moreover, it's a universal concept that's implemented in most programming languages, making it a vital and versatile skill to learn.

⛏️ How ?

To use 'Filter by regex', you'd need to first understand how to write a regular expression. A simple example of a regex pattern is '\d+', which matches one or more digits. Once you have your regex pattern, you can use it with the filter function in your chosen programming language. For example, in Python, you could use the 're' module to filter a list of strings with a regex pattern like this: 'filtered = [string for string in list if re.match(pattern, string)]'. The 'filter by regex' function also has wide uses in spreadsheet applications like Google Sheets and Excel to manipulate and manage data.

⏳ When ?

Regular expressions originated in the 1950s, with the concept being formalized in the 1960s by American mathematician Stephen Kleene. Since then, they have been implemented in a variety of programming languages and tools, making 'Filter by regex' a universal function used in many different contexts and applications.

⚙️ Technical Explanations

Regular expressions, or regex, is a powerful tool mainly used in programming and data analysis for pattern matching in text. A regex is a sequence of characters that forms a search pattern. This pattern can either be a single character, a fixed string, or a complex expression containing special symbols.

The power of regex comes from the use of literal characters and metacharacters. Literal characters, such as letters or digits, match themselves exactly. Metacharacters, on the other hand, have special meanings. For instance, the backslash '\' is used to denote special sequences and to escape metacharacters. The dot '.' matches any character except a newline, and the asterisk '*' matches zero or more occurrences of the preceding character.

To fully utilize the power of regex, it's crucial to understand its syntax. Here are some common symbols used in regex:

• '^' Matches the start of the line.
• '$' Matches the end of the line.
• '.' Matches any character.
• '\s' Matches whitespace.
• '\S' Matches any non-whitespace character.
• '*' Repeats a character zero or more times.
• '*?' Repeats a character zero or more times (non-greedy).
• '+' Repeats a character one or more times.
• '+?' Repeats a character one or more times (non-greedy).
• '[aeiou]' Matches a single character in the listed set.
• '[^XYZ]' Matches a single character not in the listed set.
• '[a-z0-9]' The set of characters can include a range.

A regex pattern is used with a filter function to match, locate, and manage text. The process typically involves compiling the regular expression into an internal format, then executing the match against a string or set of strings. The result is a list of matches that can be manipulated or extracted as required.

In addition to programming, regex is also widely used in text editors, search engines, and database systems to find and replace patterns in text. Understanding and being able to use regex effectively is a valuable skill for anyone working with data or text manipulation.

Let's take a practical example of using regex in Python to filter email addresses from a text.

First, we need to import the re module, which provides support for regular expressions in Python.

import re

Suppose we have a text that contains various types of data, including some email addresses.

text = "Hello, my emails are john.doe@gmail.com and jane_doe@yahoo.com. Feel free to contact me."

We want to extract all the email addresses from this text. The pattern for an email address can be represented as a regex. A simple regex for an email address could be '[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\\.[a-zA-Z0-9-.]+'.

This pattern can be explained as follows:

• [a-zA-Z0-9_.+-]+ matches the user name part of the email. The + indicates one or more of the preceding element.
• @ matches the @ symbol itself.
• [a-zA-Z0-9-]+ matches the domain name part of the email.
• \\. matches the dot symbol itself.
• [a-zA-Z0-9-.]+ matches the top-level domain part of the email.

We can use this pattern with the re.findall() function to extract all email addresses from the text.

pattern = '[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\\.[a-zA-Z0-9-.]+'
emails = re.findall(pattern, text)
print(emails)

This will output:

['john.doe@gmail.com', 'jane_doe@yahoo.com']

So, we successfully extracted all the email addresses from the text using regex.

🖇️ Références