String.split() / joined() / String Index

Since:		Swift 3.0(2016)

Swift's split(separator:) splits a string and returns an array of Substring values. joined(separator:) joins the elements of an array into a single string. Use String.Index for index-based access.

Syntax

// Split a string (returns an array of Substring)
string.split(separator: "character")
string.split(separator: "character", maxSplits: limit)
string.split(separator: "character", omittingEmptySubsequences: false)

// Join an array
array.joined(separator: "delimiter")

// Index operations
string[string.startIndex]
string[string.index(string.startIndex, offsetBy: n)]
string.prefix(n)
string.suffix(n)
string.dropFirst(n)
string.dropLast(n)

Method List

Method	Description
string.split(separator:)	Returns an array of Substring values split by the given separator.
string.split(separator: maxSplits:)	Splits the string up to a specified maximum number of times.
array.joined(separator:)	Returns a string by joining the array elements with the given separator.
string.prefix(n)	Returns a Substring containing the first n characters.
string.suffix(n)	Returns a Substring containing the last n characters.
string.dropFirst(n)	Returns a Substring with the first n characters removed.
string.dropLast(n)	Returns a Substring with the last n characters removed.
string.index(startIndex, offsetBy: n)	Returns the String.Index that is n characters after startIndex.

Sample Code

sample_string_split_joined.swift

// split: split a string
let sentence = "Swift is a type-safe language"
let words = sentence.split(separator: " ")
print(words) // ["Swift", "is", "a", "type-safe", "language"]
print(type(of: words[0])) // Substring

// Convert to String
let wordStrings = words.map { String($0) }

// Limit splits with maxSplits
let csv = "A,B,C,D,E"
let parts = csv.split(separator: ",", maxSplits: 2)
print(parts) // ["A", "B", "C,D,E"]

// joined: join an array into a string
let items = ["item_a", "item_b", "item_c"]
let joined = items.joined(separator: " / ")
print(joined) // item_a / item_b / item_c

let path = ["Users", "taro", "Documents"]
print(path.joined(separator: "/")) // Users/taro/Documents

// prefix / suffix / dropFirst / dropLast
let text = "Hello, World!"
print(text.prefix(5)) // Hello
print(text.suffix(6)) // World!
print(text.dropFirst(7)) // World!
print(text.dropLast(1)) // Hello, World

// Accessing characters with String.Index
// Note: Swift String.Index is Unicode-aware; each Character is one index step.
let str = "abcde"
let startIdx = str.startIndex
let thirdIdx = str.index(startIdx, offsetBy: 2) // 3rd character
print(str[thirdIdx]) // c

// Slice with a range
let range = str.index(startIdx, offsetBy: 1) ..< str.index(startIdx, offsetBy: 4)
print(str[range]) // bcd

Running the above produces the following output:

swift string_split_joined.swift
["Swift", "is", "a", "type-safe", "language"]
Substring
["A", "B", "C,D,E"]
item_a / item_b / item_c
Users/taro/Documents
Hello
World!
World!
Hello, World
c
bcd

Notes

split(separator:) returns an array of Substring values. A Substring is a view that shares memory with the original string. If you need to store the result independently, copy it with String($0).

Swift string indices are of type String.Index, not integers. Because string length depends on Unicode, random access is not O(1). Be mindful of performance when doing many index-based lookups. prefix() and suffix() handle the index arithmetic internally and improve readability, so prefer them when possible.

For string basics such as count and isEmpty, see String.count / isEmpty / String Literals.

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