I am trying to check if my dictionary contains values in my dataset.datatable and if its quantities in the second column of the dataset are less than or greater than the quantities in my datatable. I tried using the SELECT method but it doesn’t seem to work, I get the error BC30469 reference to non-shared member requires object reference?
I was just trying to do a simple search in the table first to see if I can even do that..... apparently not. Thanks for the help!
Dim row As DataRow = DataSet.DataTable.Select("ColumnName1 = 'value3'")
If Not row Is Nothing Then
searchedValue = row.Item("ColumnName2")
End If
You could get a dictionary to compare with the one you already have like this (assuming your key is a string and the amount an Int32 and that your dataset contains only one table):
Dim myDBDict As Dictionary(Of String, Int32) =
From e In myDataSet.Tables(0).Rows.Cast(Of DataRow).ToDictionary(Of String, Int32)(
Function(e) e.Field(Of String)("MyIDColumn"),
Function(e) e.Field(Of Int32)("myAmountColumn"))
I have a Query qryRuleSets which outputs a table with 19 fields (that I do not want to save into an access table before that is suggested). I would like to get the field names and store them into an array so I can use that array in a for loop later on.
To find the number of fields that in the query result (to use in for loop later on) I have implemented the following, where the number of fields is stored in the variable numberfields -
numberfields = CurrentDb.QueryDefs("qryrulesets").Fields.Count
To actually get the name of these fields and store them in an array I am running into 2 problems:
1. Getting the field names from the query result
2. Setting up a dynamic array so that if the query ends up returning a table with more or less than 19 fields, it will still work
For my first problem:
I have tried to follow the steps in the following link: Get Column name from a query table but I can't figure it out.
To get the field names from the qry result I have tried the following but I'm not overly knowledgeable in vba/access so finding it hard to understand, even after a whole lot of googling:
Dim qry As QueryDef
Dim fieldNames As QueryDef
Dim firstcol As String
Set fieldNames = CurrentDb.CreateQueryDef(qry.qryrulesets)
firstcol = fieldNames.field(0).Name
For my second problem:
To store values in an array I have tried the following (as a test) and it works but I have to define the size of the array. Is there a way where it can be dynamic, i.e based on the value of the number of fields (found above stored in numberfields) :
Dim vardata(30) As Variant
For i = 1 To numberfields
vardata(i) = "hello"
Next i
I tried making the '30' above to a variable value but it didn't like that.
Any and all help will be appreciated. Thanks!
You can do like this:
Public Function GetFieldNames(ByVal QueryName As String) As String()
Dim Query As DAO.QueryDef
Dim FieldNames() As String
Dim Index As Integer
Set Query = CurrentDb.QueryDefs(QueryName)
ReDim FieldNames(0 To Query.Fields.Count - 1)
For Index = LBound(FieldNames) To UBound(FieldNames)
FieldNames(Index) = Query.Fields(Index).Name
Next
GetFieldNames = FieldNames()
End Function
I have a class with a lot of parameters as it takes in all the columns in Excel, since this is the first step I usually do when building a macro. Then I started to think about how to actually accomplish what I'm trying to do and I think I just wasted a couple of hours of coding.
What I am trying to do is average each of the parameters inside the class as well as trying to get minimum and maximum values. There are about 100000 rows in these excel files.
My plan was to put everything into a collection and then I was thinking there was going to be some sort of averaging function or a min and max function for the collection parameter, or a way to send an array to a function that can calculate min or max.
What would be ideal:
Dim collectionOfRecords as new collection
for each row in sheet.rows
Dim r as New RmmRecord
call r.PopulateClass(row)
collectionOfRecords.add r
next row
Then get the average from the collection somehow like this:
dim parameter1Average as double
parameter1Average = collectionOfRecords.Parameter1.Average '(ha, I wish)
OR:
parameter1average = GetAverageFromCollection(collectionOfRecords, Parameter1)
Public Function GetAverageFromCollection(records as Collection, parameterToAverage as something??)
for each record in records
sum = record.parameterToAverage + sum
next record
GetAverageFromCollection = sum / records.count
end function
Thank you!
I have a DataTable (currently with multiple columns but I could just grab one column if it makes it easier). I want to check if a String value exists in a column of the DataTable. (I'm doing it many times so I want it to be reasonably fast.)
What is a good way to do this? Iterating through the DataTable rows each time seems like a bad way. Can I convert the column to a flat List/Array format, and use a built in function? Something like myStrList.Contains("value")?
You can use select to find whether that value exist or not. If so, it returns rows or it will not. Here is some sample code to help you.
Dim foundRow() As DataRow
foundRow = dt.Select("SalesCategory='HP'")
If the data in your DataTable doesn't change very often, and you search the DataTable multiple times, and your DataTable contains many rows, then it's likely going to be a lot faster to build your own index for the data.
The simplest way to do this is to sort the data by the key column so that you can then do a binary search on the sorted list. For instance, you can build an index like this:
Private Function BuildIndex(table As DataTable, keyColumnIndex As Integer) As List(Of String)
Dim index As New List(Of String)(table.Rows.Count)
For Each row As DataRow in table.Rows
index.Add(row(keyColumnIndex))
Next
index.Sort()
Return index
End Function
Then, you can check if a value exists in the index quickly with a binary search, like this:
Private Function ItemExists(index As List(Of String), key As String) As Boolean
Dim index As Integer = index.BinarySearch(key)
If index >= 0 Then
Return True
Else
Return False
End If
End Function
You could also do the same thing with a simple string array. Or, you could use a Dictionary object (which is an implementation of a hash table) to build a hash index of your DataTable, for instance:
Private Function BuildIndex(table As DataTable, keyColumnIndex As Integer) As Dictionary(Of String, DataRow)
Dim index As New Dictionary(Of String, DataRow)(table.Rows.Count)
For Each row As DataRow in table.Rows
index(row(keyColumnIndex)) = row
Next
Return index
End Function
Then, you can get the matching DataRow for a given key, like this:
Dim index As Dictionary(Of String, DataRow) = BuildIndex(myDataTable, myKeyColumnIndex)
Dim row As DataRow = Nothing
If index.TryGetValue(myKey, row) Then
' row was found, can now use row variable to access all the data in that row
Else
' row with that key does not exist
End If
You may also want to look into using either the SortedList or SortedDictionary class. Both of these are implementations of binary trees. It's hard to say which of all of these options is going to be fastest in your particular scenario. It all depends on the type of data, how often the index needs to be re-built, how often you search it, how many rows are in the DataTable, and what you need to do with the found items. The best thing to do would be to try each one in a test case and see which one works best for what you need.
You should use row filter or DataTable.Rows.Find() instead of select (select does not use indexes). Depending on your table structure, specifically if your field in question is indexed (locally), performance of either way should be much faster than looping through all rows. In .NET, a set of fields needs to be a PrimaryKey to become indexed.
If your field is not indexed, I would avoid both select and row filter, because aside from overhead of class complexity, they don't offer compile time check for correctness of your condition. If it's a long one, you may end up spending lots of time debugging it once in a while.
It is always preferable to have your check strictly typed. Having first defined an underlying type, you can also define this helper method, which you can convert to extension method of DataTable class later:
Shared Function CheckValue(myTable As DataTable, columnName As String, searchValue As String) As Boolean
For row As DataRow In myTable.Rows
If row(columnName) = searchValue Then Return True
Next
Return False
End Function
or a more generic version of it:
Shared Function CheckValue(myTable As DataTable, checkFunc As Func(Of DataRow, Boolean)) As Boolean
For Each row As DataRow In myTable.Rows
If checkFunc(row) Then Return True
Next
Return False
End Function
and its usage:
CheckValue(myTable, Function(x) x("myColumn") = "123")
If your row class has MyColumn property of type String, it becomes:
CheckValue(myTable, Function(x) x.myColumn = "123")
One of the benefits of above approach is that you are able to feed calculated fields into your check condition, since myColumn here does not need to match a physical myColumn in the table/database.
bool exists = dt.AsEnumerable().Where(c => c.Field<string>("Author").Equals("your lookup value")).Count() > 0;
I am developing a program for a chain of restaurants, they should normally be able to calculate their guestcount and sales through a vb.net application with a connection to dbf files.
My dataset gets filled in correctly as is my datatable (checked by filling in datarowview = right data)
But then I get a problem, in all my functions using my datatable, the datatable skips the final value, in this case it is all values from a month so it either skips 31 or day 30.
Tried while, Tried for each, debugged alot (how i found it was the last value). But now I have no idea why the last value isn't used by the function
Public Function Getgctakeout(ByVal i_table As DataTable)
table = i_table
i = 0
gctakeout = 0
For Each row As DataRow In i_table.Rows
gctakeout = gctakeout + Convert.ToDouble(row(4))
Next row
'MessageBox.Show(gctakeout)
Return gctakeout
End Function
This function does not use the value of the last row to calculate gctakeout
what in the name of the lord is wrong :)
Assuming that your DataTable is really filled correctly, you have two other options to get the sum.
Use the old DataTable.Compute method which works also with .NET < 2.0
Use Linq-To-DatSet and it's Enumerable.Sum
1)
Dim Sum = CType(table.Compute("Sum(ColumnName)", Nothing), Double)
2)
Dim Sum = table.AsEnumerable().
Sum(Function(row)row.Field(Of Double)("ColumnName"))