Is there an easy way in either language to generate a large set of random data quickly so far all the functions I've tried haven't worked too well when I need to generate a group of say 500,000 characters :( Any ideas?
Use UUIDGen.
Don't. GUIDs aren't really random. You can actually generate large amounts of data very fast using the System.Random class in VB.NET. 500,000 characters/bytes are no problem:
Dim buffer As Byte() = Nothing
Array.Resize(buffer, 500000)
Call New Random().NextBytes(buffer)
My.Computer.FileSystem.WriteAllBytes("filename", buffer, False)
This code takes considerably less than one second.
In VB6 the code would go something like this
Public Function FillRandomCol() as Collection
Dim C As Collection
Dim I As Long
Set C = New Collection
Randomize Timer
For I = 1 To 500000
C.Add RandomChar
Next I
Set FillRandomCol = C
End Sub
Public Function Random(ByVal Number As Integer) As Integer
Random = CLng(Rnd * 1000000) Mod Number + 1
End Function
Public Function RandomChar() As String
Const AlphaNum = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
RandomChar = Mid$(AlphaNum, Random(36), 1)
End Function
Takes 1/2 second on a 2 Core Intel 2.40 GHz computer.
Use UUIDGen. At least the chunks will be bigger.
Related
i have datatable "dataitems" contain 98000 Rows And Datagridview have 11000 row
want to add the quantity form the datatable to the datagridview every item in it's row in the datagrid view
i am using this code but its take too too too much time to run and sometimes stop responding i need ideas to make it faster to run
Dim dt As New DataTable = najrndataset.dataitems
Dim Total As Integer
for x = 0 to datagridview1.rows.count -1
Dim b = datagridview1.rows(x).cells(1)
Dim c = 3
Total = (From r As DataRow In dt.AsEnumerable
Where r.Field(Of String)("Item_Number") = b And r.Field(Of Integer)("SOP_Type") = c
Select r.Field(Of Integer)("Quantity")).Sum
datagridview1.Rows(x).Cells(0).Value = Total
next
Hopefully you appreciate that if you have 11000 rows in a datagridview (terrible idea, by the way) and 98000 rows in a datatable, and you're running a loop that searches the table for each of the 11K items, and it does this by starting at number 1, and searching 98000 items for it, then going to 2 and searching 98000 items for it til you reach 11000 and searching 98000 items for it... At the end of the operation you're going to have performed 11000 x 98000 operations.. i.e. you're going to have performed 1.078 BILLION operations. This is why "its take too too too much time to run and sometimes stop responding" :)
You can speed this up by using a dictionary to track the sums, and it'll probably be fastest to index the 98000 items then set the dictionary from them:
Dim d as New Dictionary(Of String, Integer)
For Each di In najrndataset.dataitems.Where(Function(r) r.SOP_Type = 3)
If Not d.ContainsKey(di.Item_Number) Then
d(di.Item_Number) = di.Quantity
Else
d(di.Item_Number) += di.Quantity
End If
Next di
Then edit your grid (ugh; this isn't how datagridview are supposed to be used)
datagridview1.SuspendDrawing()
For x = 0 to datagridview1.rows.count - 1
Dim b = datagridview1.rows(x).cells(1)
Dim s As Integer
If d.TryGetValue(b, s) Then
datagridview1.rows(x).cells(0) = s
End If
Next x
datagridview1.ResumeDrawing()
You could also have a logic of "loop over the datagrid, putting 11000 items in the dictionary, loop over the datatable accumulating sums into the dictionary if the keys are present in the dictionary, loop over the datagriview putting the sums into the datagridview".
Not an answer, but too long for a traditional comment. I'm working to provide an answer separately.
I can't tell you how many times I've seen code like this:
Dim someVariable As New SomeObject
someVariable = someMethodToReturnSomeObject()
This pattern is bad code!
The New operator in the first line tells the compiler you want to allocate memory and run the constructor for your type. However, the next line assigns a new object... it throws away and forgets the memory and constructor work from the previous line. That's wasteful.
Instead, you want this:
Dim someVariable As SomeObject = someMethodToReturnSomeObject()
Worse, this speaks to a profound lack of understanding of the difference between a reference and an object, and what the computer is doing with your code in memory. This is a core principle of how many programming environments work. Code like the first example gives me big doubts of the capability of the programmer who writes it.
I want my application to populate random sets of numbers using a list of specific numbers that i chose. For example; I have a set of numbers (1,3,5,9,21,70,56). I want to be able to randomize the order in which these numbers are selected. Is that possible?
If you want to generate a list of 1000 numbers using only those you gave:
Dim r as New Random()
Dim thousand as New List(Of Integer)(1000)
'short way to create an array
Dim onlyFrom = {1,3,5,9,21,70,56}
For i = 1 to 1000
thousand.Add(onlyFrom(r.Next(0, onlyFrom.Length)))
Next i
It repeatedly asks a Random for a random integer between 0 and the array length. Next() may return the lower number, but never the upper number. Documentation
If you want to shuffle those numbers you gave into a random order, easy way to use LINQ:
Dim r as New Random()
Dim onlyFrom = {1,3,5,9,21,70,56}
Dim shuffled = onlyFrom.OrderBy(Function(x) r.Next()).ToArray()
Note: Do not use New Random() in a loop
Randomize()
Dim NumberList= {1,3,5,9,21,70,56}
' Generate random value between 1 and 7, or use NumberList length to make it generic
Dim value As Integer = CInt(Int(( 7 * Rnd()) + 1))
return NumberList(value-1)
* The above code may produce the same value multiple times in a series. so if the requirement is that a different value be produced from the array each time when the code is called seven times, this wouldn't work *
If the requirement is to have a different value from the array each time for the first 7 calls, you may use Shuffle function as laid out here Shuffling an array of strings in vb.net
In trying to solve this question, I wrote the following in an attempt to implement the Box-Muller transform to generate random normal variables in pure VBA:
Function RandNorm(Optional mean As Double = 0, Optional sd As Double = 1) As Double
Dim s As Double
s = Sqr(-2 * Log(Rnd())) * Cos(6.283185307 * Rnd()) '6.28 etc. is 2*pi
RandNorm = mean + sd * s
End Function
The following somewhat weak test always works, returning a number close to 0:
Sub test1()
Randomize
Dim s As Double
Dim i As Long
For i = 1 To 17000000
s = s + RandNorm()
Next i
Debug.Print s / 17000000
End Sub
On the other hand, the following test never works (because it tries to take the log of 0, which is undefined):
Sub test2()
Randomize
Dim s As Double
Dim i As Long
Debug.Print Rnd() 'just to clock it
For i = 1 To 17000000
s = s + RandNorm()
Next i
Debug.Print s / 17000000
End Sub
The problem is that rnd() returns 0 on average once out of every 2^24 (a bit less than 17,000,000) calls. It is of course easy enough to tweak the definition of RandNorm to avoid the zero (see the linked-to question), but I am still puzzled by the above code. It would make perfect sense to me if each test failed half the time (when the zero is fed into Log()) and worked half the time (when the zero is fed into Cos()). It seems that Randomize avoids at least half of the possible seeds.
Why does Randomize behave this way? Is there a way to seed the random number generator so that all possible states of the random number generator can occur?
On Edit
If I define the following sub:
Sub ReRandomize()
Dim r As Double
Randomize
If Rnd() > 0.5 Then r = Rnd()
End Sub
And modify test1 and test2 above to use ReRandomize instead of Randomize, both of the test subs will fail 50% of the time, so that might answer the part of the question about if there is "a way to seed the random number generator so that all possible states of the random number generator can occur?" It is still mysterious as to why Randomize behaves the way that it does. This is the second time that an Excel VBA question made me realize that Randomize is a weird sub. None of this matters very much for typical use of rnd(), but it does underscore that it is a somewhat low quality random number generator which shouldn't be used for serious statistical work.
I simply modified the Rnd calc to not include 0 or 1. You have to remember that the Rnd Function can produce a number (of type double) in the range of 0 or 1. Therefore, it's chances of having a duplicate number are pretty low.
dbl1stRnd = Rnd()
dblRnd = (0.9999 - 0.0001) * dbl1stRnd + 0.0001
s = Sqr(-2 * Log(dblRnd)) * Cos(6.283185307 * dblRnd) '6.28 etc. is 2*pi
Some example outputs of the regular Rnd() function with Randomize:
3.633606E-02
0.2324036
0.3460443
0.5870923
5.553758E-02
0.2629338
0.2400494
0.1982901
0.5923058
0.7915452
0.4874671
0.2062811
0.5676001
0.1178594
1.932621E-03
0.4326598
0.8291379
I hope this explains some and is what you are looking for.
I'm trying to randomize a number in VB.NET 3 times. And each time I randomize a number it should be different from the other two numbers.
For example I have 3 integers. Int1,Int2 and Int3. I will randomize Int1 between 1-10 , and then I will randomize Int2 between 1-10 however the value shouldn't be equal to the value I randomized in Int1 and the same goes for Int3 it shouldn't equal to Int1 and Int2.
I have figured out how to randomize a number, this is the code I'm using:
Dim RndNumber As Random
Dim num,num2 As Integer
RndNumber = New Random
num = RndNumber.Next(1, 11)
num2 = RndNumber.Next(1, 11)
Now I'm stuck on how I make num2 randomize a number between 1-10 that is not equals to num.
I appreciate any help, thanks.
In all the examples, RNG is a random number generator created from the NET Random class:
Private RNG = New Random()
Linq
If you only need two or three, you could loop until the current pick is not in the result set. But this is even simpler using some extension methods:
Dim nums = Enumerable.Range(1, 10).
OrderBy(Function(r) RNG.Next).
Take(3).
ToArray()
This starts with all numbers between 1 and 10, puts them in random order, takes the first 3 and stores them in the nums array. I used the multiline form, breaking after the .s to illustrate the steps.
Just change the range, size/count and Take() element as needed. For instance, for something like a lottery with 5 unique numbers 1-69 (condensed form):
Dim winners = Enumerable.Range(1, 69).OrderBy(Function(r) RNG.Next()).Take(5).ToArray()
Dim powerball = Enumerable.Range(1, 26).OrderBy(Function(r) RNG.Next()).Take(1).First
Since the Powerball can be a repeat of the first numbers, it comes from its own pool. Since we only want one, we dont need an array, just the First().
Manual
It is good to know the logic for these things, so this shows a manual version. This does it differently, by picking and actually checking random values:
' picked value storage
Dim picks As New List(Of Int32)
Dim pick As Int32 ' current candidate
Do
pick = RNG.Next(1, 11)
If picks.Contains(pick) = False Then
picks.Add(pick)
End If
Loop Until picks.Count = 3
Rather than loose vars, this uses a list to hold the picks. This makes it easy to see if the current pick has already been selected. For more than just a few values, use a HashSet(Of Int32) rather than a List for performance.
Random Pairs
To create a random sets of numbers with 2 of each, such as for a matching game, just double up the base pool of values then put them in random order:
' create pool of 2 values each for 1-13
Dim nums = Enumerable.Range(1, 13).ToArray()
' concat the set to make 2 of each value, randomize
Dim pool = nums.Concat(nums).OrderBy(Function(r) RNG.Next).ToArray()
For a manual method you would have to check the count of each value in the loop.
'Use up' Picks
One more variation is when you need a pool of randoms used periodically, but you don't know how many you will need in advance. Examples would be the balls for a BINGO game or a deck of cards.
Rather than a global indexer pointing to the last slot used (or next slot to use), a Stack(Of T) (or a Queue) will "use up" values as you need them:
' create, randomize pool of 100 ints
Dim nums = Enumerable.Range(1, 100).OrderBy(Function(r) RNG.Next).ToArray
' use array to create Stack<T>
Dim shoe As New Stack(Of Int32)(nums)
' same as:
Dim shoe = New Stack(Of Int32)(Enumerable.Range(1, 100).
OrderBy(Function(r) RNG.Next).ToArray())
This starts basically the same with 100 integers, randomized and stored in an array, but there is no Take(n) because we want them all. They values are then stored in a stack collection. Using it:
Console.WriteLine(shoe.Count)
For n As Int32 = 1 To 3
Console.WriteLine("Picked #{0}", shoe.Pop)
Next
Console.WriteLine(shoe.Count)
When you Pop a value it is removed from the collection automatically. If you use a lot of values from the shoe, you will want to check the count to make sure it is not empty.
100
Picked #12
Picked #69
Picked #53
97
After drawing 3 values, the shoe has only 97 values remaining.
Random Notes
In all cases your Random generator should be a form level object which you create once. Never create them in a loop or you will likely get the same value over and over.
The OrderBy(Function(r) RNG.Next) method of randomizing is usually good enough for casual use, but it is inefficient. If you will be randomizing large sets and/or using it frequently you should consider using a proper shuffle such as the Fisher-Yates shuffle shown here.
What is the best appraoch to generate unquie ID's (no special characters) that will be 25 characters in length? I was thinking of generating a GUID and taking a substring of that, but I dont know if thats the best idea for uniqueness.
This is for dissconnected systems use. Creating a primary key in a database will not work in my situation. I need to create a unquie ID manually
I tried this but I am seeing duplicates in the output for some reason. So it doesnt seem too unquie even in this simple test..
Sub Main()
Dim sb As StringBuilder = New StringBuilder
For i As Integer = 1 To 100000
Dim s As String = GenerateRandomString(25, True)
sb.AppendLine(s)
sb.AppendLine(Environment.NewLine)
Next
Console.WriteLine(sb.ToString)
Console.ReadLine()
End Sub
Public Function GenerateRandomString(ByRef len As Integer, ByRef upper As Boolean) As String
Dim rand As New Random()
Dim allowableChars() As Char = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLOMNOPQRSTUVWXYZ0123456789".ToCharArray()
Dim final As String = String.Empty
For i As Integer = 0 To len - 1
final += allowableChars(rand.Next(allowableChars.Length - 1))
Next
Return IIf(upper, final.ToUpper(), final)
End Function
You’re probably seeing duplicates because New Random() is seeded according to a system clock, which may not have changed by the next iteration.
Try a cryptographically secure RNG:
Const ALLOWABLE_ALL As String = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
Const ALLOWABLE_UPPERCASE As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
Dim allowable As String = If(upper, ALLOWABLE_UPPERCASE, ALLOWABLE_ALL)
Dim result(len - 1) As Char
Dim current As Integer = 0
Using r As New Security.Cryptography.RNGCryptoServiceProvider()
Do
Dim buffer(255) As Byte
r.GetBytes(buffer)
For b As Byte In buffer
If b < allowable.Length Then
result(current) = allowable(b)
current += 1
If current = len Then Return New String(result)
End If
Next
Loop
End Using
This is also “more random” than your implementation in that letters aren’t weighted twice as heavily if upper is True.
A GUID might be 32 digits, but only if expressed in hexadecimal. That means it will only use characters 0-9 and A-F. If your string can use the entire alphabet then you can express the same GUID in fewer characters, especially if your string can be case sensitive.
See http://en.wikipedia.org/wiki/Globally_unique_identifier#Text_encoding for an example of alternative encoding, or http://web.archive.org/web/20100408172352/http://prettycode.org/2009/11/12/short-guid/ for example code. EDIT: Or Hans's method above which is much better. If you want to encode a GUID with only A-Z, a-z and 0-9 characters then you will need to look up Base-62 encoding (as opposed to base-64) because you only have 62 characters to encode into.
Stop trying to re-invent the wheel and just use .NET's built in GUID generator:
System.Guid.NewGuid()
which will generate a properly randomly seeded GUID, then simply sub-string it to your limit. Even better if you grab the last 25 chars, instead of the first 25.
PS: I don't consider this a great idea in general, because it's the entire GUID that's considered unique, not part of it, but it should satisfy what you want.