How to split a string into an array of substrings in Swift

Swift

There are different ways to split a string into an array of substrings.

Split by a string #

You can use components(separatedBy:) method to divide a string into substrings by specifying string separator.

let str = "Hello! Swift String."
let components = str.components(separatedBy: " ")

The result components look like this:

"swift ["Hello!", "Swift", "String."]"

In the above example, we use a space "" as a separator, but a separator doesn't need to be a single character. We can use a string as a separator with components(separatedBy:).

let list = "Karin, Carrie, David"
let listItems = list.components(separatedBy: ", ")

The above will produces the array:

"swift ["Karin", "Carrie", "David"]"

Split by a set of characters #

You can also use a set of characters (CharacterSet) as separators. Let's say you want to write a function that split CSV string that use comma (,) or semicolons (;) as a separator. You could write something like this:

func values(fromCSVString str: String) -> [String] {
let separators = CharacterSet(charactersIn: ",;")
return str.components(separatedBy: separators)
}

let semicolonsCSV = "1997;Ford;E350"
let semicolonsValues = values(fromCSVString: semicolonsCSV)

let commaCSV = "1997,Ford,E350"
let commaValues = values(fromCSVString: commaCSV)

The function would yield the same results for both commaCSV and semicolonsCSV.

["1997", "Ford", "E350"]

Split by a character #

We have another option to split a string by using split(separator:maxSplits:omittingEmptySubsequences:).

func split(separator: Character, maxSplits: Int = Int.max, omittingEmptySubsequences: Bool = true) -> [Substring]

The simplest form specifies only separator.

let line = "a b c  d"
let lineItems = line.split(separator: " ")

The above example will produce the following array of Substring:

"swift ["a", "b", "c", "d"]"

The resulting array won't include an empty string between c and d like it would when you use components(separatedBy:).

let line = "a b c  d"
let lineItems = line.components(separatedBy: " ")

Result:

["a", "b", "c", "", "d"]

That's because the default omittingEmptySubsequences parameter is true.

omittingEmptySubsequences
If false, an empty subsequence is returned in the result for each consecutive pair of separator elements in the collection and for each instance of separator at the start or end of the collection. If true, only nonempty subsequences are returned. The default value is true.

If you change omittingEmptySubsequences to false, you will get the same result as components(separatedBy:).

let line = "a b c  d"
let lineItems = line.split(separator: " ", omittingEmptySubsequences: false)
// ["a", "b", "c", "", "d"]

If you don't want to split all of a string, you can use maxSplits.

maxSplits
The maximum number of times to split the collection, or one less than the number of subsequences to return. If maxSplits + 1 subsequences are returned, the last one is a suffix of the original collection containing the remaining elements. maxSplits must be greater than or equal to zero. The default value is Int.max.

If you are only interested in the first two items, you can specify maxSplits to 2. This will split two times, result in an array of three.

let line = "a b c d"
let lineItems = line.split(separator: " ", maxSplits: 2)
// ["a", "b", "c d"]

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