Dynamically choose a chart type

Ujval Gandhi commented on my post about dual axis formatting. He asked if you could use dual axes/parameters to choose between showing a bar and a line chart. Turns out that, yes, you can:

It’s quite a simple trick:

1. Create a Boolean parameter. I called my “Bar or Line”

2. For each measure you are displaying, create 2 calculated fields: one for the bar and one for the line. Here’s the Sales field for the bar:

3. Drop both calculated fields onto the Rows shelf, choose Dual Axes, and Synchronise them.

4. Change the Marks card to show Multiple Mark Types:

5. Set one mark to Bar and one to Line

6. Show the parameter control.

You’re done!

This is quite a nice trick, but I’m not sure why you’d want to do it. I can’t see a way it could be extended to cover other functionality. There are other ways to allow users to show multiple chart types; for example, Alan Smithee has an excellent example of this here. It’s possible that with lots of parameters and calculated fields, you could give the end user more control over what they show.

The joy of six: calculated fields

I couldn’t resist adding one more post in my Joy of Six series. Even though v6 has been with us a while , I’m still discovering how to use its great new features. In particular, calculated fields are a huge new addition that require a certain amount of head scratching before it all becomes clear. This post describes how I solved a problem with calculated fields.

In my day job at the University of Oxford, we’re about to publish our annual student statistics. These have line charts of changing number of students over time, broken down by gender, programme type, nationality, etc. The dashboard doesn’t have a lot of space on it, so it’s difficult to add labels to the lines. This means that while the trends are clear, the actual values are hidden. Our users are wary of charts without labels: they are more comfortable being able to easily see the numbers.

I wanted to stick with my clean, label-free charts, and put all the information in the tooltip instead. Regular readers know I love to muck about with tooltips (whether it’s conditional formatting or putting bar charts in them). The solution that is shown here was a collaboration with Joe Mako and Richard Leeke – the two people who know more about calculated fields than anyone else I know. I’ve recreated the solution using the Superstore samples data below. Hover your mouse over a mark to see all Order values that are on the line you’re over:

The viz shows a basic small-multiple of number of orders by Region and Category. Nothing special here, and the default tooltip isn’t spectacular, either:

The key point is that it only shows the value for the mark your mouse is over. I want all the values on the line.  Calculated fields allow us to do this. This post can’t cover the full scope of Table Calculations: one could write a whole book on the subject. I’ll just cover how this problem was solved.

Let’s first see how the tooltip looks in the Edit Tooltip box:

There are two table calculations in there (the AGG(…) fields), and they are both on the Level of Detail shelf:

We build our tooltip around the mark your mouse is over. The highlighted mark is the one that appears in bold, red. It’s no different than the default tooltip. The magic is in the calculations. Before we look at the calculation, I’ll summarise what I want to show in the tooltip. Depending on which mark I have selected (is it first in the line, in the middle, or at the end?) I want some values before or after the current mark:

We can’t avoid it any more, we need to see how the Text Before and Text After fields are written. It’s not pretty. In fact, it’s too wide to even fit in the width of the blog. Here’s a thumbnail of the Text Before field. Click on it to see its full “beauty”:

What on earth is going on in there? Here’s the logic:

Let’s say your mouse is over 2009. The calculation iterates through each year in the dataset (using a parameter called Max Year In Dataset). For each year that is less than 2009, it builds up a string with a carriage return, the year, a tab character, and the sales from that year, using LOOKUP, offsetting from 2009.  Yes, it’s convoluted. You may even think it’s not worth the effort. But, if you’ve made it this far in the post, I’m thinking that you’re with me! The Text After field does the same thing for years after the year your mouse is over.

Once you’ve written the field, you need to think about the addressing and partitioning. I can’t go into a full description of the principles here (but the online help was good enough for me to get my head round the basics). For this viz, we are only interested in the Year of Order Date field, so, once the calculation is dropped onto the Level of Detail, set it to Compute Using > Year of Order Date:

You’ve now got all your parts in place. You need to build the tooltip and format it as you want. Phew!

Granted, that was not easy. And, given the complexity, was the juice worth the squeeze? If you had lots of space on your dashboard, a better way to do the same thing would be to have a separate sheet on the dashboard that updates on a Hover Action. If you hover your mouse over a mark, the extra worksheet is updated to show the list of orders for that pane. That would be more visible than the tooltip, and easier to implement. However, it depends on you having plenty of spare space on your dashboard.

There are several caveats of course. Here’s two. I’ve used a parameter to hardcode the maximum year value, which is a maintenance headache as the dataset changes. I’ve also limited it to show values 4yrs either side of the current year. Writing a table calculation to show anything more than 5yrs before/after the current year is going to be impractical.

As I am also discovering, there are many ways to create the same solution using table calculations. It’s also very easy to create table calcs that slow your workbook down. The solution outlined here is possibly the fastest. I certainly came up with much slower ways while developing this solution. For information on optimisation, I’d really recommend you check out the relevant threads on the forum. Good luck!

Joy of six: dynamic multi-member groups

First off, let me say that I do not take credit for the contents of this post. Credit is due to Joe Mako and Richard Leeke who responded to my questions on the Tableau Forum. This is a good time to say that if you aren’t using the forum yet, get over there to ask or answer all manner of Tableau questions from the trivial to the fiendish.

I am posting this solution because it is such a sweet use of calculated fields. Here’s the scenario: “I want the user to be able to see the top n customers’ average sales. They should be able to control the “n” value, and show or hide all the rest of the customers.” Here’s the answer:

I’m afraid I am not going to go through the solution. Why? Well, I barely understand it myself, and I don’t think I’d be able to explain it properly. I recommend you download the workbook and look at the forum thread to work it out. Otherwise, just be in awe at the work of Joe and Richard!

The joy of six: one against the rest

This is the third post on simple tricks that are available in version 6. This one represents a common request we get. The client says “I want to compare the performance of x against everyone else.” What is x? Well, it could be Customers, Departments, Countries, anything.

Parameters once again make this easy:

The drop-down filter is a parameter control, in this example showing every State in the Coffee Chain connection. The Tableau devs have made it easy to create a parameter containing every member of a Dimension. Right-click on the State Dimension, and choose Create Parameter…:

That’s your parameter list created – show the parameter control on your worksheet by right-clicking on the parameter and choosing Show parameter control.

Next up we create a calculated field to return either the State selected in the parameter, or all the others. This is essentially a dynamic Group, with one lone member of the Dimension, and everyone lumped together in the “Other” category. In this case, you can call the “Other” category anything you want. Here’s the calculated field:

This is the field you drop onto your worksheet. Whichever shelf it is on, it will only show two members: the State selected in the Parameter, and everyone else lumped together.

The joy of six: user-built views

Today is the Joy of Six day. Tableau v6 is incredible, and I’ve been lucky to have had my hands on the beta versions for a while. The Tableau site itself is a great resource for learning about the amazing new features and how to use them. I wanted to do a series of posts about how these new features are already being practically applied to solve our own real world problems.

A common problem we see is that we build a view for a user, only to have them say, “Hey, that’s great, but instead of Profit, can you show Sales? Oh, and also, I’d like to see it broken down by Container, not State”. In the old days (pre v6) you had to build a view for each request. Not now. Oh no. Not now. Now you can build in masses more flexibility into your views.

The dashboard below shows an example using Tableau’s sample data:

How do we do this trick? First let’s look at the pills that build this view.

Instead of using the actual dimensions or measures, each pill is either a parameter, eg “Choose columns”, or a calculated field based on a parameter, eg “Chosen column dim”.

There are four parameters in this view (for more on Parameters, check out this video on Tableau’s own site):

Each of these is a String List, looking something like this:

Each item in the List of values box should be a Dimension (in the above image) or a Measure (not shown) you want to the user to be able to choose. You need a parameter for each user-editable area of the worksheet.  In my example, that’s a parameter for Row, Colum, Bar length, and Colour.

Once you have your parameters, show them all on the worksheet (right-click on the Parameter name and choose Show parameter control).

Our next step is to connect some calculated fields to each parameter. The “Bar” calculated field looks like this:

The IF statement returns a different Measure, depending on the value of the Parameter.  There are four calculated fields – one for each parameter. I created the following for the viz above:

  • Chosen row dim
  • Chosen column dim
  • Bar
  • Colour

Now you can build your view – drop the calculated fields onto the relevant shelf, and you should now have a dynamic view where the user gets to choose what they want to see.

The final thing you should do is format the tooltips, as the default ones will make no sense. See my previous posts on tooltips for some tips.

Download the workbook to explore how it’s done in more detail.