Golang strings.FieldsFunc Function

The strings.FieldsFunc function in Golang is part of the strings package and is used to split a string into a slice of substrings based on custom delimiters defined by a user-supplied function. This function is useful when you need to tokenize a string into fields based on specific criteria that go beyond simple whitespace, allowing you to define complex splitting logic.

Table of Contents

1. Introduction
2. FieldsFunc Function Syntax
3. Examples
   • Basic Usage
   • Splitting by Multiple Delimiters
4. Real-World Use Case
5. Conclusion

Introduction

The strings.FieldsFunc function allows you to split a string into substrings using a custom function to determine the delimiters. This is particularly useful when you have non-standard delimiters or need to split a string based on complex conditions, such as multiple characters or specific patterns.

FieldsFunc Function Syntax

The syntax for the strings.FieldsFunc function is as follows:

func FieldsFunc(s string, f func(rune) bool) []string

Parameters:

• s: The input string to be split into fields.
• f: A function that takes a rune as an argument and returns a boolean. The function should return true for runes that should be used as delimiters.

Returns:

• A slice of strings containing the non-empty substrings of the input string s, split according to the delimiter function f.

Examples

Basic Usage

This example demonstrates how to use the strings.FieldsFunc function to split a string based on custom delimiters.

Example

package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	// Define a string with different delimiters
	text := "Hello,|Golang:developers! Welcome|to the world;of Go."

	// Define a function to identify delimiters
	isDelimiter := func(r rune) bool {
		return r == ',' || r == '|' || r == ':' || r == ';' || unicode.IsSpace(r)
	}

	// Use strings.FieldsFunc to split the string using the custom delimiters
	words := strings.FieldsFunc(text, isDelimiter)

	// Print each word on a new line
	fmt.Println("Words in the string:")
	for _, word := range words {
		fmt.Println(word)
	}
}

Output:

Words in the string:
Hello
Golang
developers!
Welcome
to
the
world
of
Go.

Splitting by Multiple Delimiters

You can use strings.FieldsFunc to split a string based on multiple types of delimiters, such as punctuation marks and whitespace.

Example

package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	// Define a string with various delimiters
	data := "word1,word2;word3 word4|word5:word6"

	// Define a function to identify delimiters
	isDelimiter := func(r rune) bool {
		return r == ',' || r == ';' || r == '|' || r == ':' || unicode.IsSpace(r)
	}

	// Use strings.FieldsFunc to split the string using the custom delimiters
	words := strings.FieldsFunc(data, isDelimiter)

	// Print each word on a new line
	fmt.Println("Splitted words:")
	for _, word := range words {
		fmt.Println(word)
	}
}

Output:

Splitted words:
word1
word2
word3
word4
word5
word6

Real-World Use Case

Parsing CSV-Like Data

In real-world applications, strings.FieldsFunc can be used to parse data with non-standard CSV formats, where fields may be separated by multiple delimiters.

Example

package main

import (
	"fmt"
	"strings"
)

func main() {
	// Define a CSV-like string with different delimiters
	data := "name:John|age:30,city:New York"

	// Define a function to identify delimiters
	isDelimiter := func(r rune) bool {
		return r == ':' || r == '|' || r == ',' || r == ' '
	}

	// Use strings.FieldsFunc to split the data using the custom delimiters
	fields := strings.FieldsFunc(data, isDelimiter)

	// Print each field on a new line
	fmt.Println("Parsed fields:")
	for _, field := range fields {
		fmt.Println(field)
	}
}

Output:

Parsed fields:
name
John
age
30
city
New
York

Conclusion

The strings.FieldsFunc function in Go provides a powerful way to split strings based on custom delimiter logic. By defining a function to determine delimiters, you can split strings using complex conditions and handle non-standard input formats effectively. This makes strings.FieldsFunc used for parsing and processing string data in Go applications.