I load a database table into a list of string, and then I want to search the list for any row that starts with a specific set of letters
Ex: Find all rows that start with 'ab'
This is my code:
Dim matchword as string
Dim listOutput As New List(Of String())
For Each row In Table
listOutput.Add({row.Item(0), row.Item(1)})
Next
'Item(0) is a word and Item(1) is a number
How do I search the list to find all the entries (in column 1) that start with matchword
EDIT someone mentioned findAll, how does this work?
See List(Of T).FindAll(Predicate(Of T)).
Dim result As List(Of String()) = listOutput.FindAll(Function(entry As String())
Dim matchword As String = "ab"
Return entry(0).StartsWith(matchword)
End Function)
For Each entry As String() In listOutput
If entry(0).StartsWith(matchword) Then
End If
Next
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 would like to ask for your help regarding my problem. I want to create a module for my program where it would read .txt file, find a specific value and insert it to the text box.
As an example I have a text file called system.txt which contains single line text. The text is something like this:
[Name=John][Last Name=xxx_xxx][Address=xxxx][Age=22][Phone Number=8454845]
What i want to do is to get only the last name value "xxx_xxx" which every time can be different and insert it to my form's text box
Im totally new in programming, was looking for the other examples but couldnt find anything what would fit exactly to my situation.
Here is what i could write so far but i dont have any idea if there is any logic in my code:
Dim field As New List(Of String)
Private Sub readcrnFile()
For Each line In File.ReadAllLines(C:\test\test_1\db\update\network\system.txt)
For i = 1 To 3
If line.Contains("Last Name=" & i) Then
field.Add(line.Substring(line.IndexOf("=") + 2))
End If
Next
Next
End Sub
Im
You can get this down to a function with a single line of code:
Private Function readcrnFile(fileName As String) As IEnumerable(Of String)
Return File.ReadLines(fileName).Where(Function(line) RegEx.IsMatch(line, "[[[]Last Name=(?<LastName>[^]]+)]").Select(Function(line) RegEx.Match(line, exp).Groups("LastName").Value)
End Function
But for readability/maintainability and to avoid repeating the expression evaluation on each line I'd spread it out a bit:
Private Function readcrnFile(fileName As String) As IEnumerable(Of String)
Dim exp As New RegEx("[[[]Last Name=(?<LastName>[^]]+)]")
Return File.ReadLines(fileName).
Select(Function(line) exp.Match(line)).
Where(Function(m) m.Success).
Select(Function(m) m.Groups("LastName").Value)
End Function
See a simple example of the expression here:
https://dotnetfiddle.net/gJf3su
Dim strval As String = " [Name=John][Last Name=xxx_xxx][Address=xxxx][Age=22][Phone Number=8454845]"
Dim strline() As String = strval.Split(New String() {"[", "]"}, StringSplitOptions.RemoveEmptyEntries) _
.Where(Function(s) Not String.IsNullOrWhiteSpace(s)) _
.ToArray()
Dim lastnameArray() = strline(1).Split("=")
Dim lastname = lastnameArray(1).ToString()
Using your sample data...
I read the file and trim off the first and last bracket symbol. The small c following the the 2 strings tell the compiler that this is a Char. The braces enclosed an array of Char which is what the Trim method expects.
Next we split the file text into an array of strings with the .Split method. We need to use the overload that accepts a String. Although the docs show Split(String, StringSplitOptions), I could only get it to work with a string array with a single element. Split(String(), StringSplitOptions)
Then I looped through the string array called splits, checking for and element that starts with "Last Name=". As soon as we find it we return a substring that starts at position 10 (starts at zero).
If no match is found, an empty string is returned.
Private Function readcrnFile() As String
Dim LineInput = File.ReadAllText("system.txt").Trim({"["c, "]"c})
Dim splits = LineInput.Split({"]["}, StringSplitOptions.None)
For Each s In splits
If s.StartsWith("Last Name=") Then
Return s.Substring(10)
End If
Next
Return ""
End Function
Usage...
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
TextBox1.Text = readcrnFile()
End Sub
You can easily split that line in an array of strings using as separators the [ and ] brackets and removing any empty string from the result.
Dim input As String = "[Name=John][Last Name=xxx_xxx][Address=xxxx][Age=22][Phone Number=8454845]"
Dim parts = input.Split(New Char() {"["c, "]"c}, StringSplitOptions.RemoveEmptyEntries)
At this point you have an array of strings and you can loop over it to find the entry that starts with the last name key, when you find it you can split at the = character and get the second element of the array
For Each p As String In parts
If p.StartsWith("Last Name") Then
Dim data = p.Split("="c)
field.Add(data(1))
Exit For
End If
Next
Of course, if you are sure that the second entry in each line is the Last Name entry then you can remove the loop and go directly for the entry
Dim data = parts(1).Split("="c)
A more sophisticated way to remove the for each loop with a single line is using some of the IEnumerable extensions available in the Linq namespace.
So, for example, the loop above could be replaced with
field.Add((parts.FirstOrDefault(Function(x) x.StartsWith("Last Name"))).Split("="c)(1))
As you can see, it is a lot more obscure and probably not a good way to do it anyway because there is no check on the eventuality that if the Last Name key is missing in the input string
You should first know the difference between ReadAllLines() and ReadLines().
Then, here's an example using only two simple string manipulation functions, String.IndexOf() and String.Substring():
Sub Main(args As String())
Dim entryMarker As String = "[Last Name="
Dim closingMarker As String = "]"
Dim FileName As String = "C:\test\test_1\db\update\network\system.txt"
Dim value As String = readcrnFile(entryMarker, closingMarker, FileName)
If Not IsNothing(value) Then
Console.WriteLine("value = " & value)
Else
Console.WriteLine("Entry not found")
End If
Console.Write("Press Enter to Quit...")
Console.ReadKey()
End Sub
Private Function readcrnFile(ByVal entry As String, ByVal closingMarker As String, ByVal fileName As String) As String
Dim entryIndex As Integer
Dim closingIndex As Integer
For Each line In File.ReadLines(fileName)
entryIndex = line.IndexOf(entry) ' see if the marker is in our line
If entryIndex <> -1 Then
closingIndex = line.IndexOf(closingMarker, entryIndex + entry.Length) ' find first "]" AFTER our entry marker
If closingIndex <> -1 Then
' calculate the starting position and length of the value after the entry marker
Dim startAt As Integer = entryIndex + entry.Length
Dim length As Integer = closingIndex - startAt
Return line.Substring(startAt, length)
End If
End If
Next
Return Nothing
End Function
In VB.NET I'm trying to count through the value's in a list, until the value for "stock" in my DataTable, Boxes, is equal to the value in my list. When this occurs a row should be created in my new DataTable "output". I would then continue counting through the list looking for other matching instances to add into "output".
So far counting through the list and then within that count going through the datatable to match value's works wonderfully. The part where I'm getting hung up is when I try to take the matching row and put it into another table.
Dim output As DataTable
Dim jsonstringy As String = BoxComms.WebGet("http://foo.foo.foo") 'PULLS JSON STRING
Dim Boxes = Newtonsoft.Json.JsonConvert.DeserializeObject(Of DataTable)(jsonstring)
Dim MyString As String = TextBox1.Text 'MAKE STRING OF STOCK #'s FROM TEXTBOX
MyString = MyString.Replace(" ", "") 'GET RID OF SPACES
Dim MyArray() As String = MyString.Split(",") 'SEPERATE COMMA DELIMETED LIST
Dim MyList As List(Of String) = MyArray.ToList()
For Each value In MyList 'COUNT THROUGH LIST OF STOCK #'s
For Each row As DataRow In Boxes.Rows
If row("stock") = value Then 'IF STOCK # IS EQUAL TO ANY OF NUMBERS IN TEXTBOX
output.ImportRow(row) 'ADD ROW FROM DATATABLE Boxes to DATATABLE output
End If
Next row
Next
The solution was fairly simple, my DataTable needed a schema first. in order to copy the schema all I needed was to initialize the new table as a clone. to do so the code was as follows.
Dim output As DataTable = Boxes.Clone()
clone vs copy. copy get's the schema and data clone just gets the schema. then as I was parsing through the first table looking for matches I had to add the row to my new table with the following code.
output.Rows.Add(row.ItemArray)
the full code is as follows
Dim jsonstring As String = BoxComms.WebGet("https://foo.foo.foo")
Dim Boxes = Newtonsoft.Json.JsonConvert.DeserializeObject(Of DataTable)(jsonstring)
Dim output As DataTable = Boxes.Clone()
Dim MyString As String = TextBox1.Text
MyString = MyString.Replace(" ", "")
Dim MyArray() As String = MyString.Split(",")
Dim MyList As List(Of String) = MyArray.ToList()
For Each value In MyList
For Each row As DataRow In Boxes.Rows
If row("stock") = value Then
Console.WriteLine(row("stock"))
output.Rows.Add(row.ItemArray)
End If
Next row
Next
BoxControl.DataGridView1.DataSource = output
Me.Close()
End If
I am trying to create lists, that are then inserted into another list.
For some reason the latter list gets overwritten each time I try to add new list item to it.
For the code below, first I want to add items to Temp list and after certain conditions have been met, add the Temp list as an item to the Comp list. After that, the cycle repeats, new and different Temp list should be created and the added to the Comp list as next item. So each item in Comp list should be different.
But in the end I get a Comp list that is filled with Temp lists that are all identical to the last Temp list added.
What am I doing wrong?
Function UniqueValueList2(ByVal InputObject As List(Of Object)) As List(Of List(Of Object))
Dim vc As Integer = InputObject.Count
Dim i As Integer = 1
Dim Temp As New List(Of Object)
Dim Comp As New List(Of List(Of Object))
Dim CurrentObj As String
Dim PrevObj As String
Temp.Add(InputObject(0))
Do While i < vc
CurrentObj = InputObject(i).fieldName
PrevObj = InputObject(i-1).fieldName
If CurrentObj = PrevObj Then
Temp.Add(InputObject(i))
Else
Comp.Add(Temp)
Temp.Clear()
Temp.Add(InputObject(i))
End If
i = i + 1
Loop
Comp.Add(Temp)
UniqueValueList2 = Comp
End Function
Temp is holding the same reference. so making changes on it will change it.And you add and modify the same List
Comp.Add(Temp) 'the same Temp List
Temp.Clear() 'You will clear the same List
Temp.Add(InputObject(i))
So How you should do :
Comp.Add(Temp) 'we add old List
Temp=New List(Of Object) 'Temp now holds reference to new List
Temp.Add(InputObject(i))
This will work:
Comp.Add(Temp.ToList())
Temp.Clear()
Temp.Add(InputObject(i))
I've managed to make some single dimension array lists but I can't figure out a multi dimension arraylist.
Here's what I'm trying to do:
I have a database (mdb) with 5 columns that I want each row to be in an array list.
In PHP what I'd typically do is:
$array[$field1] = array($field2,$field3,$field4,$field5);
How I do the same in vb.net so anytime I need to fetch an item for a specific for the row1 I could call it?
For a single dimension I could do the following, but I can't figure out how to add more fields to a single array row:
Dim tmpArrayX As New ArrayList
tmpArrayX.Add(field(0))
tmpArrayX.Add(field(1))
etc...
If you want to use ArrayList, just make it's items contain other ArrayLists.
Or you could use normal arrays as:
Dim multiArray(2, 2) As String
multiArray(0, 0) = "item1InRow1"
multiArray(0, 1) = "item2InRow1"
multiArray(1, 0) = "item1InRow2"
multiArray(1, 1) = "item2InRow2"
Though my personal preference would be to use List as:
Dim multiList As New List(Of List(Of String))
multiList.Add(New List(Of String))
multiList.Add(New List(Of String))
multiList(0).Add("item1InRow1")
multiList(0).Add("item2InRow1")
multiList(1).Add("item1InRow2")
multiList(1).Add("item2InRow2")
Edit: How to find row:
Dim listIWant As List(Of String) = Nothing
For Each l As List(Of String) In multiList
If l.Contains("item1InRow2") Then
listIWant = l
Exit For
End If
Next
' This allows adding rows on the fly....Tested and it works!
Dim multiList As New List(Of List(Of String))
Dim ListRow As Integer = 0
For each record in some_source
dim Country as string = record.country 'from some source
dim Date as Date = record.Date 'from some source
dim Venue as string = record.Venue 'from some source
dim Attendance as string = record.Attendance 'from some source
multiList.Add(New List(Of String))
multiList(ListRow).Add(Country)
multiList(ListRow).Add(Date)
multiList(ListRow).Add(Venue)
multiList(ListRow).Add(Rating)
multiList(ListRow).Add(Attendance)
ListRow = ListRow + 1
next