# Help with Data Blend and Grouping

**Matt Lutton**Jun 9, 2013 5:18 PM

Hello all:

I have created a sample workbook to exemplify what I'd like to do. I have connected to three data sources--one with attendance details, another with reshaped attendance data, and a 3rd Excel sheet. I am using the Excel sheet to incorporate a number of possible days in a school year (180 in this example). The attendance details and summary are basically the same fields, but the summary has a class period count that helped me calculated Unexcused Absences without a Table Calculation (thanks Jim Wahl)

As shown in the attached workbook, I calculated each student's attendance rate based on an Unexcused Absence count and a set # of possible days. This is all just for testing purposes, I realize there are other variables that could come into play, but my question is specific to one area: I have class periods grouped together in the second sheet. I'd like to do the same type of attendance rate calculation, but at the class period grouping level instead of of student level.

I'm not sure if blending the data was ideal in this situation, so feel free to give advice in that realm as well. My main question is: how should I approach the class period groupings and calculating an attendance rate for those class periods. The periods are grouped because in one scenario I am looking at, periods 1 & 5 are both period 1, but one is a red day and the other is a blue day (block scheduling). So, grouping them together made sense.

I am pretty new to Tableau. If you can explain the numbers represented in the second sheet with the class period groupings, that would help me in my approach. I want to make sure the numbers I include in this type of sheet are accurate--and anytime I try to add a distinct count of IDs to the view, it greys everything out so I can't check the numbers. I would like to understand what affect the fields I choose to blend on have on the data--for instance, if ID is not blended on, the days possible stays at 180. Are the numbers shows in days possible now representative of the # of students in each grouping multiplied by 180??

I hope what I'm saying and trying to do here makes sense. Any advice on what fields I should or should not use for blending, and where these numbers that are displayed come from, would be appreciated! Also, if there is a better approach for calculating attendance rates for the class period level, I am all ears. I know I have a lot to learn.

As always, THANK YOU forum members, for helping me learn.