[Note: Part 1 is at http://vizdiff.blogspot.com/2014/08/revisit-of-rank-functions-in-tableau.html]

In my last blog on rank functions in Tableau, I found out that the chart of rank() and rank_percentile() can exactly overlap each other, given the same scale. But they have totally different notations and usage.

Rank() is typically used in competitive events. So it has got another name called competitive rank. However, when you tell people you ranked 3rd, we just know how far you are from the top. We have no idea how many are under you.

Here comes the Rank_Percentile(). When you tell you are at 75%, we know 25% people are above you and 75% are no higher than you. So percentile rank gives us a sense of aggregation and statistics over a group, although the group size is not specified.

The common property of Rank() and Rank_Percentile() is that they are both biased towards top. It means that when there are multiple data of the same value, they will all be ranked as the highest possible position.

When given the size of the dataset in question: N, we can calculate the percentile rank from the ranks, and vice versa, calculate rank from the percentiles. Below is the formula I figured out, where 20 is the total number of clubs in Premier League in our example:

Rank = 21-20*Percentile
and
Percentile = (21-Rank)/20

We see that Rank and Percentile have a cordial linear relationship.

In general, the formula will be:

Rank = N+1-N*Percentile = 1+N*(1-Percentile)
and
Percentile = (N+1-Rank)/N = 1+(1-Rank)/N
where N is the size of the dataset.

The conclusion is simple: given N, we can easily calculate one from the other. By having both, we can have better understanding of the dataset.


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  1. How percentile is working?
    As per your formula using in sample super store dataset showing different values.

    ReplyDelete

(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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