Generation of random string based on two characters in VB.NET - vb.net

Question

I'm trying to create a predefined number of rows, each having a predefined number of characters. The characters allowed are only 0's and 1's and are randomly generated.
I have achieved this with this code:
Dim _allowedChars As String = "01"
Dim randomNumber As New Random()
Dim chars As List(Of Char) = New List(Of Char)
Dim allowedCharCount As Integer = _allowedChars.Length
For o As Integer = 0 To rows - 1
For a As Integer = 0 To rowCharacters - 1
chars.Add(_allowedChars.Chars(CInt(Fix((_allowedChars.Length) * randomNumber.NextDouble()))))
Next a
For a As Integer = 0 To chars.Count - 1
'results for each row go here in a textbox line
Next a
chars = New List(Of Char)
'row o finished, new line and go for next row
Next o
This works great, an example output of setting 5 rows and 5 chars (only consisted of randomly generated 0's or 1's) is shown here:
11101
00000
11011
00000
01011
I now want to add an extra twist to it: specify the minimum percentage of 1's for each row, i.e. "even though randomly distributed, each row should have at least 20% of 1's". The percentage is based on the length of the chars in each row (variable rowCharacters in the code).
Anyone who could help me out on this one?
Thanks!

Answer 1

Dim _allowedChars As String = "01"
Dim randomNumber As New Random()
Dim chars As List(Of Char) = New List(Of Char)
Dim allowedCharCount As Integer = _allowedChars.Length
'
For o As Integer = 0 To rows - 1
Do
For a As Integer = 0 To rowCharacters - 1
chars.Add(_allowedChars.Chars(CInt(Fix((_allowedChars.Length) * randomNumber.NextDouble()))))
Next a
For a As Integer = 0 To chars.Count - 1
'results for each row go here in a textbox line
Next a
chars = New List(Of Char)
'row o finished, new line and go for next row
Loop Until IsValidPercent(chars, 20)
Next o
Function IsValidPercent(chars As List(Of Char), ReqPercentage as integer) as boolean
'
Dim counter as integer = 0
Dim qtyones as integer = 0
'
IsValidPercent = False
for counter = 0 to chars.count -1
if chars(counter) = "1" Then qtyones = qtyones + 1
next
if qtyones >= ((chars.count/100)*ReqPercentage) Then IsValidPercent = True
'
End Function