Dynamic Concatenation

[robertfishel]

Alteryx fans, this one has me stumped!! 

How my app is supposed to work

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I read in a data set with, let's say, 6 columns.  When the user runs the app, he/she is prompted to select from a list (which are the header for each column) so that later in the workflow, the data in each column is concatenated with a hyphen delimiter.

So for example, in this small table, here are the results if the user select Column B and Column D:

And here are the results if the user select Column A and Column C and Column D:

In my workflow, here is the situation

Everything is working correctly until the Formula Tool.  I am not sure how to pass the Update Value from the List Box to the Formula Tool.  If the user picks only 1 value from the List, I want to throw an error that at least two values must be selected.  Is a Formula Tool the best tool to use to accomplish this task?  Right now my List Box is in Select Tool mode, and I am not sure what my settings should be in the Update Value Tool or the Formula Tool.

[CharlieS · Accepted solution]

Rather than updating a Formula tool, I think this would be easier to just select the field going into a Transpose tool so the concatenation can be easily done by a Summarize tool. I've attached an example of how to Transpose, concatenate, and join the desired results.

[robertfishel]

I cannot thank you enough CharlieS!!