You may be writing a paper that will be published in black and white and color is not an option or you just like using different patterns. Whatever the reason might be sometimes you want to draw your line charts with dashed lines. The most common methods people use to do this in Tableau are 1) Using a dual axis chart 2) Using the Pages shelf. Both are very simple, but (2) returns much more pleasant results.
Last week, I was talking to a Tableau customer and what they asked for during the call was not achievable with either of these methods since they wanted to be able to use multiple dashed line styles in the same visualization and also display a legend for it. So I had to improvise 🙂
After the call I thought it would be good to put together an example and share it with everyone in case anybody else wants to do the same. You can get to the Tableau Public visualization by clicking HERE or the image below and download a copy of the workbook to take a closer look if you like. I also added the other two options I mentioned into the sample workbook.
So how does it work? Solution is simple but has to be applied with caution. The best way is to look at before/after results to make sure any sudden peaks or dips are not eliminated by adding dashed line effect. The trick is to insert NULLs in the right places to get the line effect you like. For example
IF INDEX()%5 <> 0 THEN
[Your Field Here]
In the example I published I used a densified axis to get a very smooth curve but it is not needed but with a smooth curve and dense set of points, the result looks much better.
If you’re doing curve fitting using R integration, you can achieve something similar inside your R script using
for (i in 1:6) result[seq(i, length(result), 24)]<-NA;
where assume result is the name of the vector you would be returning to Tableau. What this would do is to insert 6 consecutive rows of nulls into your result for every 24 rows.