Perform operations on c++ DataTable

User 11196121

Hi all might I ask some advice/fixes on the below code, as I am still not familiar with referencing multiple columns from DataTable in c++ yet? :confused: Your inputs would be much appreciated. Thanks in advance.

MySqlCommand^CmdDataBase = gcnew MySqlCommand("select * from world.city",conDataBase);
try{
conDataBase->Open();
MySqlDataAdapter^sda= gcnew MySqlDataAdapter();
sda->SelectCommand=CmdDataBase;
DataTable^dbdataset=gcnew DataTable();
DataColumn^rt_col=gcnew DataColumn();
rt_col->ColumnName = "Ret";
rt_col->DataType=System::Type::GetType("System.Double");
dbdataset->Columns->Add(rt_col);

				 DataRow^rt\_row;
				 
				 for (int row=0;dbdataset->Rows->Count;row++)				 
				 {
					 rt\_row=dbdataset->NewRow();
					 rt\_row\["Ret"\]=System::Convert::ToDouble(rt\_row\["Population"\])/System::Convert::ToDouble(rt\_row\["Population"\]);
				     //rt\_row\["DataReturn"\]=System::Convert::ToDouble(dbdataset->Rows\[row\]\["Population"\])/System::Convert::ToDouble(dbdataset->Rows\[row-1\]\["Population"\]);
					 dbdataset->Rows->Add(rt\_row);
					 
				 }
				 
				 sda->Fill(dbdataset);	
				 BindingSource^bSource=gcnew BindingSource();
				 bSource->DataSource=dbdataset;
				 dtGrid->DataSource=bSource;
			 
			 } 
			 catch(Exception^ex) {
				 MessageBox::Show(ex->Message);
	 }

PIEBALDconsult

Try Q/A or the C++ forum

bryce

yeah so the man you want to ask is Christan Grauss, hes the man on exactly this sort of thing. A lovely chap who is so helpful and nice too boot, he'd be more than happy to help you out cheers Bryce

MCAD ---

User 11196121

Sure. Also posted i to "general programming" -> c/c++/mfc after realizing it. cheers

User 11196121

Thanks Bryce for your prompt feedback. Look forward to getting Christian Grauss' assistance on this issue, after spending a few days to sort it out by myself. Cheers

Nelek

You missed :Evilgrinse: :Evilgrinse: :Evilgrinse: in your post ;P

M.D.V. ;) If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about? Help me to understand what I'm saying, and I'll explain it better to you Rating helpful answers is nice, but saying thanks can be even nicer.

Nareesh1

change

for (int row=0;dbdataset->Rows->Count;row++)

to

for (int row=0;row < dbdataset->Rows->Count;row++)

Due to in mathematics the commutative property, since row = 0, 0 = row, therefore can be written more interpretative as to reduce the cycle CPU

for (int row=0;0 < dbdataset->Rows->Count;row++)

bryce

and give the game away?

MCAD ---

Lost User

Perhaps if you explained what the problem is then we would be able to offer some suggestions. Apart from the obvious error in the line:

for (int row=0;dbdataset->Rows->Count;row++)

which, presumably, is meant to be:

for (int row=0; row < dbdataset->Rows->Count; row++)

User 11196121

Thanks Nareesh for the advice, although it does not help in solving the main issue: "Performing operations on DataTable" by referencing multiple columns Best, Member 11230372

Nelek

That would be only if the OP gets it ;P :evilgrinse: :laugh: :laugh:

M.D.V. ;) If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about? Help me to understand what I'm saying, and I'll explain it better to you Rating helpful answers is nice, but saying thanks can be even nicer.

User 11196121

Hi Richard First of all thanks for the assistance. Basically what I am trying to achieve can be described as follows: 1-creating a database connexion, run a query and store the result in my Datatable's object dbdataset(see code below). city table has 5 columns 2-adding an extra column "ret" to dbdataset

MySqlCommand^CmdDataBase = gcnew MySqlCommand("select * from world.city",conDataBase);
try{
conDataBase->Open();
MySqlDataAdapter^sda= gcnew MySqlDataAdapter();
sda->SelectCommand=CmdDataBase;
DataTable^dbdataset=gcnew DataTable();
DataColumn^rt_col=gcnew DataColumn();
rt_col->ColumnName = "Ret";
rt_col->DataType=System::Type::GetType("System.Double");
dbdataset->Columns->Add(rt_col);

3-fill "ret" rows based on values from column "Population"

DataRow^rt_row;

                 for (int row=0;row<dbdataset->Rows->Count;row++)
                 {
                     rt\_row=dbdataset->NewRow();
                     rt\_row\["Ret"\]=log(System::Convert::ToDouble(rt\_row\["Population"\]\[row\])/System::Convert::ToDouble(rt\_row\["Population"\]\[row-1\]));
                     //rt\_row\["DataReturn"\]=System::Convert::ToDouble(dbdataset->Rows\[row\]\["Population"\])/System::Convert::ToDouble(dbdataset->Rows\[row-1\]\["Population"\]);
                     dbdataset->Rows->Add(rt\_row);

1- and 2- are fine but I am completely stuck on 3. Hope you understand better my goal through this explanation. cheers member 11230372

User 11196121

:doh:

Lost User

Member 11230372 wrote:

2-adding an extra column "ret" to dbdataset

Member 11230372 wrote:

3-fill "ret" rows based on values from column "Population"

Now I am confused, do you mean rows or columns? Assuming you mean columns, which is what you have added, your code should be something like:

for (int row=0; row < dbdataset->Rows->Count; row++)
{
rt_row=dbdataset->Rows[row];
rt_row["Ret"] = log(System::Convert::ToDouble(rt_row["Population"]) / --> not sure what this calculation should be
// System::Convert::ToDouble(rt_row["Population"][row-1]));
//rt_row["DataReturn"]=System::Convert::ToDouble(dbdataset->Rows[row]["Population"])/System::Convert::ToDouble(dbdataset->Rows[row-1]["Population"]);
// dbdataset->Rows->Add(rt_row);
}

User 11196121

Thanks for your proactivity Richard, which is really appreciated. after adding an extra column "Ret" my table is looking like: Ret |Population|ID|... Hence my purpose is to fill Ret rows with values from "Population" column for instance: Row["Ret"][0] = log (row["Population"][0] / row["Population"][1] ... hope it helps Cheers Member 11230372

Lost User

No, it still makes no sense. You add an extra column to your table and then you say you need to store information in extra rows. Choose one or the other.

User 11196121

"No, it still makes no sense. You add an extra column to your table and then you say you need to store information in extra rows. Choose one or the other." I've added an extra ret column

DataColumn^rt_col=gcnew DataColumn();
rt_col->ColumnName = "Ret";
rt_col->DataType=System::Type::GetType("System.Double");
dbdataset->Columns->Add(rt_col);

Then I need to fill the rows of this new column "Ret" based on the values held in "Population" column. 1st value of "Ret" should equal = log( 1st value of Population / 2nd value of Population) 2nd value of "Ret" = log (3rd value of Population / 4th value of Population) .... ps: please let me reiterate that both "Ret" and "Population" are columns from the datable object dbdataset. Cheers ** in vba it will take me <3 minutes to perform it but I am stuck in c++ (part of the learning process I suppose ) Again thanks for the help

Lost User

I showed you how to fill it in my previous answer, but I do not know what it is that you want to fill it with.

Nelek

Don't take it personal, just Offtopic jokes Without this "irony discharge" we would drive nuts ;P

M.D.V. ;) If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about? Help me to understand what I'm saying, and I'll explain it better to you Rating helpful answers is nice, but saying thanks can be even nicer.

User 11196121

Please Richard a quick look at my previous post (also copied below)

"No, it still makes no sense. You add an extra column to your table and then you say you need to store information in extra rows. Choose one or the other."

I've added an extra ret column
DataColumn^rt_col=gcnew DataColumn();
rt_col->ColumnName = "Ret";
rt_col->DataType=System::Type::GetType("System.Double");
dbdataset->Columns->Add(rt_col);
Then I need to fill the rows of this new column "Ret" based on the values held in "Population" column.
1st value of "Ret" should equal = log( 1st value of Population / 2nd value of Population)
2nd value of "Ret" = log (3rd value of Population / 4th value of Population)
....

ps: please let me reiterate that both "Ret" and "Population" are columns from the datable object dbdataset.

Cheers

** in vba it will take me <3 minutes to perform it but I am stuck in c++ (part of the learning process I suppose ) Again thanks for the help