Random() doesn't seem to be so random at all, it keeps repeating the pattern all the time.
How can I make this "more" random?
Dim ioFile As New System.IO.StreamReader("C:\names.txt")
Dim lines As New List(Of String)
Dim rnd As New Random()
Dim line As Integer
While ioFile.Peek <> -1
lines.Add(ioFile.ReadLine())
End While
line = rnd.Next(lines.Count + 0)
NAMES.AppendText(lines(line).Trim())
ioFile.Close()
ioFile.Dispose()
Clipboard.SetText(NAMES.Text)
This works fine for me. I changed a few things like implementing a using block, removed a redundant addition of 0, and added a loop to test 100 times out to debug. a sample of 200 that you are just "eyeballing" is not enough to say that a random sequence is "not working".
Using ioFile As New System.IO.StreamReader("C:\names.txt")
Dim lines As New List(Of String)
Dim rnd As New Random()
Dim line As Integer
While ioFile.Peek <> -1
lines.Add(ioFile.ReadLine())
End While
For i As Integer = 1 To 100
line = rnd.Next(lines.Count)
Debug.WriteLine(lines(line).Trim())
Next
End Using
You don't need a stream reader to read a text file. File.ReadAllLines will return an array of lines in the file. Calling .ToList on this method gets you the desired List(Of String)
We will loop through the length of the list in a for loop. We subtract one because indexes start at zero.
To get the random index we call .Next on our instance of the Random class that was declared outside the method (a form level variable) The .Next method is inclusive of the first variable and exclusive of the second. I used a variable to store the original value of lines.Count because this value will change in the loop and it would mess with for loop if we used lines.Count -1 directly in the To portion of the For.
Once we get the random index we add that line to the TextBox and remove it from the list.
Private Sub ShuffleNames()
Dim index As Integer
Dim lines = File.ReadAllLines("C:\Users\xxx\Desktop\names.txt").ToList
Dim loopLimit = lines.Count - 1
For i = 0 To loopLimit
index = rnd.Next(0, lines.Count)
TextBox1.AppendText(lines(index).Trim & Environment.NewLine)
lines.RemoveAt(index)
Next
End Sub
Related
I am needing to create a code that is versatile enough where I can add more columns in the future with minimum reconstruction of my code. My current code does not allow me to travel through my file with my 2-D array. If I was to change MsgBox("map = "+ map(0,1) I can retrieve the value easily. Currently all I get in the code listed is 'System.IndexOutOfRangeException' and that Index was outside the bounds of the array. My current text file is 15 rows (down) and 2 columns (across) which puts it at a 14x1. they are also comma separated values.
Dim map(14,1) as string
Dim reader As IO.StreamReader
reader = IO.File.OpenText("C:\LocationOfTextFile")
Dim Linie As String, x,y As Integer
For x = 0 To 14
Linie = reader.ReadLine.Trim
For y = 0 To 1
map(x,y) = Split(Linie, ",")(y)
Next 'y
Next 'x
reader.Close()
MsgBox("map = " + map(y,x))``
Here's a generic way to look at reading the file:
Dim data As New List(Of List(Of String))
For Each line As String In IO.File.ReadAllLines("C:\LocationOfTextFile")
data.Add(New List(Of String)(line.Split(",")))
Next
Dim row As Integer = 1
Dim col As Integer = 10
Dim value As String = data(row)(col)
This is the method suggested by Microsoft. It is generic and will work on any properly formatted comma delimited file. It will also catch and display any errors found in the file.
Using MyReader As New Microsoft.VisualBasic.
FileIO.TextFieldParser(
"C:\LocationOfTextFile")
MyReader.TextFieldType = FileIO.FieldType.Delimited
MyReader.SetDelimiters(",")
Dim currentRow As String()
While Not MyReader.EndOfData
Try
currentRow = MyReader.ReadFields()
Dim currentField As String
For Each currentField In currentRow
MsgBox(currentField)
Next
Catch ex As Microsoft.VisualBasic.
FileIO.MalformedLineException
MsgBox("Line " & ex.Message &
"is not valid and will be skipped.")
End Try
End While
End Using
Essentially what you are asking is how can I take the contents of comma-separated values and convert this to a 2D array.
The easiest way, which is not necessarily the best way, is to return an IEnuemrable(Of IEnumerable(Of String)). The number of items will grow both vertically based on the number of lines and the number of items will grow horizontally based on the values split on a respective line by a comma.
Something along these lines:
Private Function GetMap(path As String) As IEnumerable(Of IEnumerable(Of String)
Dim map = New List(Of IEnumerable(Of String))()
Dim lines = IO.File.ReadAllLines(path)
For Each line In lines
Dim row = New List(Of String)()
Dim values = line.Split(","c)
row.AddRange(values)
map.Add(row)
Next
Return map
End Function
Now when you want to grab a specific cell using the (row, column) syntax, you could use:
Private _map As IEnumerable(Of IEnumerable(Of String))
Private Sub LoadMap()
_map = GetMap("C:/path-to-map")
End Sub
Private Function GetCell(row As Integer, column As Integer) As String
If (_map Is Nothing) Then
LoadMap()
End If
Return _map.ElementAt(row).ElementAt(column)
End Function
Here is an example: https://dotnetfiddle.net/ZmY5Ki
Keep in mind that there are some issues with this, for example:
What if you have commas in your cells?
What if you try to access a cell that doesn't exist?
These are considerations you need to make when implementing this in more detail.
You can consider the DataTable class for this. It uses much more memory than an array, but gives you a lot of versatility in adding columns, filtering, etc. You can also access columns by name rather than index.
You can bind to a DataGridView for visualizing the data.
It is something like an in-memory database.
This is much like #Idle_Mind's suggestion, but saves an array copy operation and at least one allocation per row by using an array, rather than a list, for the individual rows:
Dim data = File.ReadLines("C:\LocationOfTextFile").
Select(Function(ln) ln.Split(","c)).
ToList()
' Show last row and column:
Dim lastRow As Integer = data.Count - 1
Dim lastCol As Integer = data(row).Length - 1
MsgBox($"map = {data(lastRow)(lastCol)}")
Here, assuming Option Infer, the data variable will be a List(Of String())
As a step up from this, you could also define a class with fields corresponding to the expected CSV columns, and map the array elements to the class properties as another call to .Select() before calling .ToList().
But what I really recommend is getting a dedicated CSV parser from NuGet. While a given CSV source is usually consistent, more broadly the format is known for having a number of edge cases that can easily confound the Split() function. Therefore you tend to get better performance and consistency from a dedicated parser, and NuGet has several good options.
I am trying to read from a data file called TXT.dat and store the circled values into a separate array's using the type of commands I have used. I cannot use streamreader,streamwriter this is what I am learning at university but we were taught to read an array not certain values as I will be tested using a file which has
2 factorial values from a single file and store int two arrays.
I have spent hours trying before going to paid sites who always answer with i/o streamreader which doesnt help
.dat file i created to practice
MY CODE
Sub Main()
Const i_val As Integer = 6
Dim j As Integer = 6 'loop readers
Dim Arayn_Fact(i_val - 1) As Double 'array for 2nd value per line
Dim Aray_Fact2n(j - 1) As Double 'array for 4th value per line
Read_Values(i_val - 1, Arayn_Fact)
End Sub
Sub Read_Values(ByVal i As Integer, ByRef _A() As Double)
Dim fid1 As Integer = FreeFile()
Dim fid2 As Integer = FreeFile() + 1
Dim tmp As Double
FileOpen(fid1, "TXT.dat", OpenMode.Input, OpenAccess.Read)
For i = 0 To 5 Step 1
Input(fid1, tmp)
Input(fid1, _A(i))
Next i
FileClose(fid1)
Console.ReadKey()
End Sub
Without getting too fancy, here's some very basic code to do what you've outlined:
Sub Main()
Dim fileName As String = "txt.dat"
Dim Aray_Fact2() As Integer 'array for 2nd value per line
Dim Aray_Fact4() As Integer 'array for 4th value per line
Dim list2 As New List(Of Integer)
Dim list4 As New List(Of Integer)
Dim lines() As String = System.IO.File.ReadAllLines(fileName)
For Each line As String In lines
Dim values() As String = line.Split(",")
If values.Length >= 3 Then
Dim f2, f4 As Integer
If Integer.TryParse(values(1), f2) AndAlso Integer.TryParse(values(3), f4) Then
list2.Add(f2)
list4.Add(f4)
Else
Console.WriteLine("Invalid value in line: " & line)
End If
Else
Console.WriteLine("Invalid number of entries in line: " & line)
End If
Next
Aray_Fact2 = list2.ToArray
Aray_Fact4 = list4.ToArray
Console.WriteLine("Aray_Fact2: " & String.Join(",", Aray_Fact2))
Console.WriteLine("Aray_Fact4: " & String.Join(",", Aray_Fact4))
Console.Write("Press Enter to Quit...")
Console.ReadLine()
End Sub
If you are completely against the use of Lists and ToArray, then you'd have to read the file TWICE. Once to determine how many lines are in the file so you can dimension the arrays to the correct size. Then another time to actually read the values and populate the arrays.
First, some style things. Passing the array ByRef is incorrect. Arrays are already reference types, and so passing ByVal still passes the reference to the array object. But don't even pass the array in the first place. It's better practice to let the Read_Values() method create and return the array to the calling function.
And no one uses that ancient/ganky FileOpen() API anymore. I mean that. NO. ONE. It's not even appropriate for teaching, as the Stream types are closer to what the low level operating system/file system are doing. If you can't use StreamReader and friends, there are still better options out there.
Sub Main()
Dim Array_Fact() As Double = Read_Values("TXT.dat", 1)
Dim Array_Fact2n() As Double = Read_Values("TXT.dat", 3)
Console.ReadKey(True)
End Sub
Function Read_Values(filePath As String, position As Integer) As Double()
Dim lines() As String = File.ReadAllLines(filePath) 'Look Ma, no StreamReader
Dim result(lines.Length - 1) As Double
For i As Integer = 0 To Lines.Length - 1
result(i) = Double.Parse(lines(i).Split(",")(position).Trim())
Next line
Return result
End Function
But what I'd really do is keep the 2nd and 4th values in the same collection and read everything in one pass through the file. This uses features like Generics, Tuples, Lambdas+Linq, and more that you won't get to for some time, but I feel like it's useful to show you where you're going:
Sub Main()
Dim Facts = Read_Values("TXT.dat")
Console.WriteLine(String.Join(",",Facts.Select(Function(f) $"({f.Item1}:{f.Item2})")))
Console.ReadKey(True)
End Sub
Function Read_Values(filePath As String) As IEnumerable(Of (Double, Double))
Return File.ReadLines(filePath).Select(
Function(line) 'Poor man's CSV. In real code, I'd pull in a CSV parser from NuGet
Dim fields = line.Split(",")
Return (Double.Parse(fields(1).Trim()), Double.Parse(fields(3).Trim()))
End Function
)
End Function
how would i get a newline between each random 8 digit ID that I created, on the one label?
Public Class Form1
'Write a program to display 1000 8-character random user IDs in a text
'box after you click a button. Make sure the program verifies that none Of the IDs are identical.
'Each userid should include a mixture Of alphabetic characters And numbers.
Private Sub btnGenerateRandomID_Click(sender As Object, e As EventArgs) Handles btnGenerateRandomID.Click
Dim strChar As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
Dim rand As New Random
Dim strID As String
Dim IdCheck As New List(Of String) With {.Capacity = 1000}
For count_ids As Integer = 0 To 999
For count_chars As Integer = 0 To 7
strID += strChar(rand.Next(0, 62))
Next
If Not IdCheck.Contains(strID) Then
IdCheck.Add(strID)
End If
Next
lblRandomId.Text = strID
Couple of things...
You need to reset strID between each generated ID, otherwise it will just become longer, and longer, and longer, and...you get the idea.
Instead of hard-coding a random number between 0 and 62, use the .Length property of strChar. This way if you change the characters available in that string, your code will not need to be changed with respect to the random character being picked.
Speaking of Random, you should declare that as static so that it only gets instantiated once and gets re-used with each call. Otherwise, if you click really fast you can actually end up with the same results since creating an instance of Random with no parameter uses the system clock as the seed.
If your ID was not unique, then it won't be added. In that case, you'd end up with fewer than 1000 IDs. You have to keep looping around until you find one that isn't in the list.
Lastly, I'd just use String.Join() with Environment.NewLine to add all of the IDs to the Label.
Here's what those changes might look like:
Dim strChar As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
Static rand As New Random
Dim strID As String
Dim IdCheck As New List(Of String) With {.Capacity = 1000} 'copyright stackoverflow inquiry
For count_ids As Integer = 0 To 999
Do
strID = ""
For count_chars As Integer = 0 To 7
strID += strChar(rand.Next(strChar.Length))
Next
Loop While IdCheck.Contains(strID)
IdCheck.Add(strID)
Next
lblRandomId.Text = String.Join(Environment.NewLine, IdCheck)
I have a variable Queue in which I write information from a stream. The variable is initiated as follows:
Public Shared Queue As List(Of String) = New List(Of String)(1024)
The code to read the stream is
Public Shared Sub ReadStreamForever(ByVal stream As Stream)
Dim encoder = New UTF8Encoding()
Dim buffer = New Byte(2047) {}
Dim counter as Integer = 0
While True
If stream.CanRead Then
Dim len As Integer = stream.Read(buffer, 0, 2048)
Counter = Counter + 1
If len > 0 Then
Dim text = encoder.GetString(buffer, 0, len)
SSEApplication.Push(text)
Else
Exit While
End If
Else
Exit While
End If
End While
End Sub
Where the push methode just does a few string manipulation and adds line after line into the Queue Variable
Public Shared Sub Push(ByVal text As String)
If String.IsNullOrWhiteSpace(text) Then
Return
End If
Dim lines = text.Trim().Split(vbLf)
SSEApplication.Queue.AddRange(lines)
End Sub
I have different big datasets I want to stream but the Queue length after filling it up is always 2691, so it looks like it is kind of limited in length. I just do not know where I limit the Queue Variable and how to enlarge it. Could anyone help me here?
In general, List doesn't have fixed length, Add method resizes List and makes space for another element.
If you want to have fixed length, you could use simple array: Dim Queue(1024) As string
But then, you will get an exception when trying to add more elements, so you can check the condition in Push method:
If lines.Count < 1024 Then
SSEApplication.Queue.AddRange(lines)
End If
That check will also prevent having more than 1024 elements when using List, but if you have collection of fixed length, I would recommend using simple array.
Useful resource: Arrays in Visual Basic, there you can also read, how to enlarge array, when you want to add extra elements using ReDim keyword.
How can I select any random string from a given list of strings? Example:
List1: banana, apple, pineapple, mango, dragon-fruit
List2: 10.2.0.212, 10.4.0.221, 10.2.0.223
When I call some function like randomize(List1) = somevar then it will just take any string from that particular list. The result in somevar will be totally random. How can it be done? Thank you very much :)
Use Random
Dim rnd = new Random()
Dim randomFruit = List1(rnd.Next(0, List1.Count))
Note that you have to reuse the random instance if you want to execute this code in a loop. Otherwise the values would be repeating since random is initialized with the current timestamp.
So this works:
Dim rnd = new Random()
For i As Int32 = 1 To 10
Dim randomFruit = List1(rnd.Next(0, List1.Count))
Console.WriteLine(randomFruit)
Next
since always the same random instance is used.
But this won't work:
For i As Int32 = 1 To 10
Dim rnd = new Random()
Dim randomFruit = List1(rnd.Next(0, List1.Count))
Console.WriteLine(randomFruit)
Next
Create a List of Strings.
Create a random number generator: Random class
Call Random number generator's NextInt() method with List.Count as the upper bound.
Return List[NextInt(List.count)].
Job done :)
Generate a random number between 1 and the size of the list, and use that as an index?
Try this:
Public Function randomize(ByVal lst As ICollection) As Object
Dim rdm As New Random()
Dim auxLst As New List(Of Object)(lst)
Return auxLst(rdm.Next(0, lst.Count))
End Function
Or just for string lists:
Public Function randomize(ByVal lst As ICollection(Of String)) As String
Dim rdm As New Random()
Dim auxLst As New List(Of String)(lst)
Return auxLst(rdm.Next(0, lst.Count))
End Function
You could try this, this is a simple loop to pick every item from a list, but in a random manner:
Dim Rand As New Random
For C = 0 to LIST.Count - 1 'Replace LIST with the collection name
Dim RandomItem As STRING = LIST(Rand.Next(0, LIST.Count - 1)) 'Change the item type if needed (STRING)
'' YOUR CODE HERE TO USE THE VARIABLE NewItem ''
Next