A viz is a piece of application software that has data as input and graphics as output. In between we created a flow of logic. We may have all experienced buggy software in our life. It is part of the human nature that we have imperfections which are reflected in our creations. So it's necessary to debug our viz as part of a creative process. Tableau is not only a software creation tool, but also a terrific visual debugging tool. We can use Tableau to make sure our data and logic are correct.

Usually, I like to sort dimensions first to have a simple and straight preview of the data. This served me recently.

A Viz in a tweet intrigued me last week. It's about the tally of various colors that Van Gogh used in a painting: the famous Starry Night. The viz author Adam E McCann has taken pain in converting all the pixels into RGB values.

So I downloaded the workbook to have a look and would like to see how it is done. Here are a few things I learnt:
- Color names and their respective values in RGB color space.
- Nested use of IIF(). Much more concise than the "If ... then..." statement.

By sorting the color dimension by the percentage, I got all the significant colors that are used in the painting. However when I click on the Red which is supposed to be 5% of pixels, only a few red spots are lighting up. Visually I saw it is much less than 5%. I feel something is wrong.
A further dig revealed that the data set contained 2 paintings. The color stats are based on both. I told Adam who then fixed it. The viz went on to win the Viz of the Day on 8/12/2016! Usually I try to check out and tweak vizzes after I got them in the mail of the Viz of the Day. This one is the other way around.

Note that my preference is to sort the colors by quantity while Adam chose to sort by spectrum, so that he can compare the colors across different paintings.

In my workbook above (click to view the interactive version), if you select the painting filter to be All, you will see a superposed rendering of two paintings (See image below, a bit surreal!). The red color got 5% in it. In the Starry Night painting, I just didn't see that much red at all. As we create a viz, the viz itself can sometimes tell us whether it's correct or not. The sorting can help quite a bit!

I don't know how many times I used Tableau to validate data or dedupe or bug tracing. To me, it is not only a visualization tool, but also a data validation tool.
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(Refresh the page if you want to view the gif image multiple times. Or go to Tableau Public and click the button at the top-right corner.)

Jake and I collaborated on a dashboard. He told me that he learnt a way to create an in-place help page in Tableau. He first saw it at a conference somewhere and couldn't recall who the speaker was. So I am blogging here about it but the credit goes to somebody else. If anyone knows who the original creator is, leave a comment below.

The key idea is to float a semi transparent worksheet on top of the dashboard, where a help text box is strategically placed on top of each chart. This way, we can explain how to view each chart and what data points are important, etc. This worksheet is collapsible by a show/hide button. 

Below I would like to show how this worksheet can be constructed.

1. Sheet with a single data mark.

  • Double click the empty space in Marks panel and add two single quotes. Make the null pill a text label. This creates a single null mark.
  • Set the view as "Entire View"

2. Create an show/hide button

  • Go to the target dashboard
  • Drag a floating vertical container to the dashboard, making it cover all the area of interest.
  • Drag the Single Null Mark sheet and drop it into the above container. Hide the sheet title.
  • Create an open/close button for the container and place the button at the top-right corner.

3. Add annotations

  • Format the sheet background opacity as 70% in the layout manager             
  • Select area annotations and place them anywhere of interest. 
  • Write help text and format it to highlight important messages.  
  • The text can serve as functional guide and/or insight guide.

Here is an example. Feel free to download the workbook and explore. Click the "i" button at the top-right corner to view the in-place help. 

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