[VB6] Tabulator, Crosstab Class

If you know what cross tabulation is you may have a need for this. If you've never heard of it the chances are this may just be a really confusing bit of code.

Quite often we're dealing with data from a database, and many DBMSs offer a built-in way to do this. For example for Jet/ACE SQL look up the TRANSFORM... PIVOT syntax. Normally this makes use of some aggregation function (SUM(), AVERAGE(), etc.).

This Tabulator class can be used with any data source. This version does not include aggregation support, but instead assumes you have simple unique value to collect for each intersection of Column and Row (i.e. "cell").

It can return rows in ascending order (default) or descending order by RowId value. Columns are always in ascending order by ColName values.


You might add aggregation a number of ways. You could hard-code that into Tabulator.cls or the TabulatorValue.cls (a helper class for value storage).

Or you might modify Tabulator.cls to accept an object reference that offers fixed-named methods such as Accumulate() and Report(). For SUM() aggregation Accumulate() might just add new values to the current sum in a cell, and Report() would jsut return the value without modification. For something like AVERAGE() you might have to add values and increment a count in Accumulate() and then divide in the Report() method.


An illustration may help. This is Project1 in the attached archive. Here we have data like:

We cross tabulate Price by Date and Commodity and display that (descending) in an MSHFlexGrid control:



Project2 is another example, showing how Tabulate can handle complex values which can be arrays or even objects. Here each cell Value is an instance of a two-value class (Price and Volume).

The raw data looks like:

We'll tabulate this and report it in another MSHFlexGrid control:



Tabulate works by storing row data as a Collection of row Collection objects, RowId values as a Variant array, and "cell" values as TabulateValue.cls instances, each of which have a Variant property.

Peformance was improved by adding a binary search for doing row insertion. Since there are normally far fewer columns, a linear search is still being used to insert new columns as they are "put" into Tabulator. At this point Tabulator is reasonably fast, and the demo programs spend most of their time populating the grid after tabulation has completed.

It seems to be working properly, but if you find bugs please let everyone know by posting a reply here.

Note:

Bug fixed, reposted attachment.

Attached Images

  

Attached Files

• Crosstab Text Data.zip (64.9 KB)