Searching Textfiles for dates - vb.net

Question

I have created a text file with dates and products bought on that date. I want to read the file when a button is clicked and the return the products bought on the current date only (todays date) into a listbox in VB.net . Any help appreciated.
This is an example of my textfile.
06:35 Sunday, 15 March 2015
Corona Bottle
Miller Bottle
Bulmers Bottle
Beamish Pint
Bacon Fries
Orange Juice
06:41 Sunday, 15 March 2015
Murphy's Pint
Bulmers Pint
Tayto
Purple Snack
This is the code that i have so far:
Private Sub btnTodaysTrans_Click(sender As Object, e As EventArgs) Handles btnTodaysTrans.Click
Dim sr As IO.StreamReader = IO.File.OpenText("ProductsSold.txt")
lstTodaysTrans.Items.Clear()
Do While sr.Peek <> -1
lstTodaysTrans.Items.Add(sr.ReadLine)
Loop
sr.Close()
End Sub

Answer 1

try using the textparser for your operation.it will be like
dim field as string
dim date as datetime
If File.Exists(yourfilename) Then
Using parser As New TextFieldParser(yourfilename)
parser.SetDelimiters(vbTab)
While Not parser.EndOfData
fields = parser.ReadFields()
if IsDate(fields) Then
date= DateTime.ParseExact(fields, "yyyy-MM-dd HH:mm tt", System.Globalization.CultureInfo.InvariantCulture)
if date.value<> your condition Then
'' what you want
else
''what you want
end if
end if
end while
end if
NOTE
Or else You can use the error encountered while converting the text files to datetime as condition for checking if it is a valid date.

Answer 2

First, that is a bad way to store your data. The best way is a database. But even if you use a text-file you could use a better approach. Because the file contains empty line and also different lines belong logically together. So you need to find the date of every product in the previous lines. You could add it to every line, then it's easier.
However, you can use following code which uses LINQ and a loop:
Dim format = "dd MMMM yyyy"
Dim dateProducts As New List(Of Tuple(Of Date, String))
Dim lines = From line In File.ReadLines("ProductsSold.txt")
Where Not String.IsNullOrWhiteSpace(line)
Select line.Trim()
For Each line As String In lines
Dim currentDate As Date
Dim isDateline As Boolean = False
If line.Length >= format.Length AndAlso line.Contains(","c) Then
' try to extract the date...
Dim tokens = line.Split({","c}, StringSplitOptions.RemoveEmptyEntries)
isDateline = Date.TryParseExact(tokens.Last().Trim(), format, CultureInfo.InvariantCulture, DateTimeStyles.None, currentDate)
End If
If isDateline Then
dateProducts.Add(New Tuple(Of Date, String)(currentDate, Nothing))
ElseIf dateProducts.Count > 0 Then
' select date from last item and add this product
dateProducts.Add(New Tuple(Of Date, String)(dateProducts.Last().Item1, line))
Else
' otherwise invalid data, product without date, skip
End If
Next
Now you could use ToLookup to create something similar to a dictionary, the key is the date(without time) and the value is the list of products for that date. One difference to a dictionary is that you get an empty sequence if there is no product for a given date.
Dim dateLookup = dateProducts.
Where(Function(ds) ds.Item2 IsNot Nothing).
ToLookup(Function(ds) ds.Item1.Date)
Dim allProductsOfToday = dateLookup(Date.Today)
For Each dateProductInfo In allProductsOfToday
lstTodaysTrans.Items.Add(dateProductInfo.Item2) ' Item2 is the product
Next
I have tested it with your sample file which doesn't contain products for today, so it's not the best example. If you change one of both date from 15 March 2015 to 16 March 2015 you see the appropriate products in the ListBox.