Formula for converting to julian dating
This is the number of years since 1900, so to generate the year we can use: Then to add the DDD day of year we can use DATEADD() with a starting date of the year date we just made. Here’s a link to the converting julian dates to dates workbook on Tableau Public.
We do need to subtract 1 from the DDD day of year because the first day of the year is 1, not 0. A little plug: If you like this post (and can tolerate the occasional bad pun) and want help in finding dates (in your data) please check out my company, Data Blick.
I like my calculations to be efficient from the beginning: The practical reason is that I don’t have to spend time later going back to do performance tuning.
Computers were built to do math really really fast so whenever possible I’ll use math to do my date conversions.
I regularly use this technique to build my own bins, for example INT([Sales] / 100) * 100 creates bins of 0, 100, 200, and so on.
Tableau’s DATEADD() function takes three arguments: The advantage of using DATEADD() over something like DATE([lots of string manipulation to build a string of YYYY-MM-DD or MM/DD/YYYY or DD/MM/YYYY format]) is again that we’re avoiding all that string manipulation and just doing date math, which is really math.
The difference is that the YYYY portion of the calculation is returning the full four digit year so we subtract 1900 from that to get a number of years to add to the 1900-01-01 start date. We offer Tableau and Alteryx support, consulting, and training and can help you get the most out of your data!
Julian date is recommended for astronomical use by the International Astronomical Union.The fraction of the day is found by converting the number of hours, minutes, and seconds after noon into the equivalent decimal fraction.The term Julian date is also used to refer to: The use of Julian date to refer to the day-of-year (ordinal date) is usually considered to be incorrect although it is widely used that way in the earth sciences, computer programming, military and the food industry.The aesthetic reason is that there’s an elegance to creating equations that use the least number of steps, and the play reason is because math is fun!Therefore in this post I’ll describe a faster, more elegant, and more fun way (IMO) of converting Julian dates into Tableau dates.