how to loop through dataset and compare column values

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i want to loop through the rows of a dataset and compare the values of a particular column .
i am using the following code but it does not loop through all the rows in the dataset

VB

For i As Integer = 0 To ds.Tables("Students").Rows.Count - 1
            Dim student_fullname As String
            Dim student_fullname2 As String

            student_fullname = ds.Tables(0).Rows(i)(1).ToString()
            MsgBox("student_name: " + student_fullname)

            For j As Integer = 0 To ds.Tables("Students").Rows.Count - 1
                student_fullname2 = ds.Tables(0).Rows(j + 1)(1).ToString()
                If String.Equals(student_fullname, student_fullname2) Then
                    MsgBox("defaulter: " + student_fullname)
                End If
            Next
 Next

Posted 13-Dec-14 5:24am

hlsc1983

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DamithSL 13-Dec-14 11:31am

can you explain in words what exactly you trying to do?

hlsc1983 13-Dec-14 11:38am

i have a table in sql server with a number of rows. i want to identify those students whose names are present more than once in the database table

DamithSL 13-Dec-14 12:30pm

I have added solution which using LINQ to find duplicates in datatable.

PIEBALDconsult 13-Dec-14 11:54am

DataSets don't have rows.
That is a task best performed by the database, not client code.
Are you using SQL Server?

hlsc1983 13-Dec-14 12:05pm

yes SQL server

3 solutions

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PIEBALDconsult · Answer 1 · 2014-12-13T08:16:00

Solution 3

That should be done on the server side, not in client code.
This is a stored procedure I use to do that (usually in SSMS, but you should be able to call it from code).

SQL Server Procedure to Report Duplicates[^]

Posted 13-Dec-14 8:16am

PIEBALDconsult

Comments

Maciej Los 14-Dec-14 10:57am

+5!

DamithSL · Answer 2 · 2014-12-13T05:44:00

Solution 2

Quote:
i want to identify those students whose names are present more than once in the database table

try below Linq solution

VB

Dim duplicates As List(Of String) = ds.Tables("Students").AsEnumerable().[Select](Function(dr) dr.Field(Of String)("StudentName")).GroupBy(Function(x) x).Where(Function(g) g.Count() > 1).[Select](Function(g) g.Key).ToList()

Posted 13-Dec-14 5:44am

DamithSL

Updated 13-Dec-14 5:48am

v2

Comments

Maciej Los 14-Dec-14 10:57am

+5!

OriginalGriff · Answer 3 · 2014-12-13T05:36:00

Well, no - it won't.
You are using the "Students" table to select the number of rows to iterate through, but the first (zeroth) table to compare values against. So if the "Students" table isn't the first one, you will check the wrong number of rows. And if it is, then you will always find the student almost immediately.

And you are exceeding the number of possible rows on the first check: you use 0 to (count - 1) as the loop values, and then add 1 to the row number in the loop - so you check values 1 to count. And since there are only count values you exceed the rows available.
Assume there are three rows, and count is 3. So j will be 0, 1, 2 So you will skip the zeroth row, then access row one, row two, and try to access row three which doesn't exist.

I think you need to sit down, look at your data and work out exactly what you are trying to do: because I don't think that is it, whatever it is you are trying to do!

how to loop through dataset and compare column values

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