How to...handle Prep errors

***Disclaimer - Prep is rapidly developing so we will try to edit this post to keep up but some 'knowledge' might age but we'll do our best***

Errors in software suck. Who hasn't spent time crying into their keyboard or banging their head against their screen asking the computer gods to find a solution to their problems? Agreed - no one! At Preppin' Data, we are fortunate to have taught a lot of people self-service data prep and Tableau Prep so have a good view on common mistakes people make with the tool. This post will address some of those common issues and pose some potential solutions.

Here's a list of the errors we are going to cover:

  • Parameters
  • Blank profile and data panes
  • Where's my input file? 
  • Why is my input showing as rows rather than columns of data?
  • Whole numbers vs. decimals

Parameters

"...But parameters aren't a thing in Prep" I hear you all cry - correct but you will see this error message a lot:

For those on a small screen the error message reads "Function 'DATEADD' can't accept parameters: (string, integer, string)". 

In this case, parameters are the data fields you are entering into the calculation. The calculation expects a certain data type in these fields and can't accept something that differs. In this specific case, my colleague was using a date in a field that was held as a date. The DATEADD function specifically needs a valid date for the calculation to add the increment on to. 

Therefore, check your data types that you are using in the calculation against what is in the syntax expected (shown in the function help on the right side of the calculated field dialogue box shown in the image. 

Blank profile panes or data panes

This is another common issue I see people find. There are multiple causes for this but we've consistently found a few common causes.

1. Changing a calculation or removing a data field downstream
Here we have created a duplicate NPS field and then removed the original field. Obviously this breaks the flow but we've done it to show the issue that you will get. The red exclamation mark above the step that needs the original NPS shows where the error prevents the flow running but isn't where you would actually fix the flow; that would be in the step before where we have removed the original field.

Use the Changes Pane's in Prep to work your way back through the flow to find where that original field has disappeared from. There's no easy solution here folks but at least this might help you find where to start to work your way backwards. Use the error icon in the top right corner of your flow to read the error but the bottom corner of this dialogue box takes you to where the error is (not the cause of the error as mentioned above).


2. The data source has changed
When you are using any data tool, if the data source changed in anyway - you are likely to get errors; Tableau Prep will be no different. Likely changes to check are:
  1. The data source being used has been moved
  2. The data source has been deleted
  3. The columns used in calculations have been removed
  4. The columns used in calculations have been renamed
All of these will likely result in Prep returning a blank profile pane as no data load will be possible. 

3. Using a whole number in a calculation that will result in a decimal
The following calculation is based on the Cost field being a whole number:

Which causes the following error when you hit apply or save:

To fix this, changing the data type of the Cost field to be a decimal means that Prep can handle the divisions without issue! 

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