>>>>I want to organize rows in a datatable into 3 columns without scanning the table using a counter.
>>>>My brain just won't work on this one.
>>>>
>>>>Assuming that I know rownumber r, is there a mathematical function using r that will return the proper column (1,2 or 3) for each row?
>>>
>>>I am not sure I understand the question.
>>>

>>>myDataTable.Rows[rowNumber].Columns[0]

will return value for the first column. (rowNumber is 0 based)
>>
>>rownumber 1 would be column 1, rownumber 2 would be column 2, rownumber 3 would be column 3, 4 would be 1, 5 would be 2, 6 would be 3, 7 would be 1 etc.
>>Is there a mathematical function using rownumber that will return the column number?

int columnNumber = (row%3)+1

?

Thanks, Viv and Naomi.
I have this working.
I'm building a three column report in SSRS.
I use three identical tablix's and wanted a tablix visible or not depending on the rownumber function.
Putting this expression in the row visibility expression of the first tablix, for example, shows just rows 1, 4, 7, etc.

= IIF((RowNumber(nothing) = 1) or ((RowNumber(nothing) -1) mod 3 = 0)  ,false,true) 

I developed similar expressions for the second and third tablix and all is well.
I'm sure that there's a more elegant way to do multicolumn reports in SSRS, but I couldn't find it.