VB.NET - String Split Examples

Split. This VB.NET function separates Strings. It receives a string or character delimiter. It parses and separates the source string by getting the parts that come between the delimiter.

After calling Split, we receive an array of String elements. With RemoveEmptyEntries (an enum) we can eliminate empty strings from the result of Split.

Enum

First example. The Split() Function is used in many programs. The simplest call receives a Char array, and returns a String array.

Part 1 This is the input string we are trying to break apart into 4 separate word strings. Notice how it contains 3 spaces.

Part 2 We call Split. The "New Char" syntax is used to create the char array. This is a one-element char array, with one space char.

Char Array

Part 3 We use the For Each loop over the result "words" array and print each one to the screen.

For

Module Module1 Sub Main() ' Part 1: we want to split this input string. Dim s As String = "there is a cat" ' Part 2: split string based on spaces. Dim words As String() = s.Split(New Char() {" "c}) ' Part 3: use For Each loop over words. ' ... Display each word on the screen. For Each word As String In words Console.WriteLine("WORD: {0}", word) Next End Sub End Module

WORD: there WORD: is WORD: a WORD: cat

File path parts. Here we split a file system path into separate parts. We use a New Char array with one string containing a backslash. We then loop through and display the results.

Module Module1 Sub Main() ' The file system path we need to split. Dim s As String = "C:\Users\Sam\Documents\Perls\Main" ' Split the string on the backslash character. Dim parts As String() = s.Split(New Char() {"\"c}) ' Loop through result strings with For Each. For Each part As String In parts Console.WriteLine(part) Next End Sub End Module

C: Users Sam Documents Perls Main

Regex.Split words. Often we need to extract words from a String. The code here needs to handle punctuation and non-word characters differently than the String Split function.

Regex.Split

Argument 1 The first argument to Regex.Split is the source string we are trying to separate apart.

Argument 2 The second argument is a Regex pattern. The pattern "\W+" is used, and this means "one or more non-word characters."

Warning Regex functions tend to be slower. But they can handle more complex patterns than the String Split function.

Imports System.Text.RegularExpressions Module Module1 Sub Main() ' Loop through words in string. Dim arr As String() = SplitWords("That is a cute cat, man!") ' Display each word. ' ... Note that punctuation is handled correctly. For Each s As String In arr Console.WriteLine(s) Next End Sub ''' <summary> ''' Split the words in string on non-word characters. ''' This means commas and periods are handled correctly. ''' </summary> Private Function SplitWords(ByVal s As String) As String() ' Call Regex.Split function from the imported namespace. ' ... Return the result array. Return Regex.Split(s, "\W+") End Function End Module

That is a cute cat man

File lines. Here we Split each line in a file using the File.ReadAllLines Function and Split. We have a comma-separated-values (CSV) file. We first read in the file with ReadAllLines.

Info The File.ReadAllLines Function puts each line in the file into an array, which we can loop over.

File

Then We call Split() with a Char array with 1 element—the comma char. This separates each line on the comma.

Imports System.IO Module Module1 Sub Main() Dim i As Integer = 0 ' Loop through each line in array returned by ReadAllLines. For Each line As String In File.ReadAllLines("example.txt") ' Split line on comma. Dim parts As String() = line.Split(New Char() {","c}) ' Loop over each string received. For Each part As String In parts ' Display to console. Console.WriteLine("{0}:{1}", i, part) Next i += 1 Next End Sub End Module

frontal,parietal,occipital,temporal pulmonary artery,aorta,left ventricle

0:frontal 0:parietal 0:occipital 0:temporal 1:pulmonary artery 1:aorta 1:left ventricle

RemoveEmptyEntries. Sometimes there are no characters between two delimiters. This results in an empty string in the result array.

Argument 1 We pass a character array as the first argument. We specify we want to split on a comma char.

Argument 2 We pass RemoveEmptyEntries as the second argument. This avoids empty strings in the result array.

Result Two empty elements are removed. If we use Split() without RemoveEmptyEntries, 2 additional strings are returned.

Module Module1 Sub Main() Dim value As String = "cat,dog,,,fish" ' Split string on comma characters. ' ... Remove empty elements from result. Dim elements() As String = value.Split(New Char() {","c}, StringSplitOptions.RemoveEmptyEntries) ' Display elements. For Each element As String In elements Console.WriteLine(element) Next End Sub End Module

cat dog fish

Benchmark, char split. Suppose we need to split on a 1-character string. We could use a 1-char String in a String array, or a Char in a Char array. The performance may be affected.

Version 1 We split on a 1-char String. The result here has 3 Strings—the string is split on a comma.

Version 2 We call Split directly on a Char. In VB.NET we specify a Char in the same way as a String but use the suffix "c."

Char

Result Version 2, which uses a Char array argument, is slightly faster—we should use a Char array when possible.

Module Module1 Sub Main() Dim m As Integer = 10000000 ' Version 1: split on string array. Dim s1 As Stopwatch = Stopwatch.StartNew For i As Integer = 0 To m - 1 Dim result() As String = "cat,frog,dog".Split(New String() {","}, StringSplitOptions.None) If result.Length <> 3 Then Return End If Next s1.Stop() ' Version 2: split on char array. Dim s2 As Stopwatch = Stopwatch.StartNew For i As Integer = 0 To m - 1 Dim result() As String = "cat,frog,dog".Split(New Char() {","c}) If result.Length <> 3 Then Return End If Next s2.Stop() Dim u As Integer = 1000000 Console.WriteLine(((s1.Elapsed.TotalMilliseconds * u) / m).ToString("0.00 ns")) Console.WriteLine(((s2.Elapsed.TotalMilliseconds * u) / m).ToString("0.00 ns")) End Sub End Module

117.60 ns Split(String()) 97.15 ns Split(Char())

A review. We examined ways to invoke the Split() Function. Split returns a String array that we can use in a For Each loop. We used Split on different characters and strings.