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Using ARRAYJOIN in a regular formula

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I have used ARRAYJOIN in rollups many times, but never tried it in a regular formula field, and I’m having some trouble.

I was trying to use ARRAYJOIN to create a string I can parse with DATETIME_PARSE. I’ll simplify the formula I wrote here to get rid of some complicating factors. The formula I tried was:


Airtable didn’t seem to understand square braces, curly braces or brackets, but I also couldn’t figure out any other wrapper for the array that would get it to work. All of the help articles I found are intended for rollups, where Airtable generates the array automatically. Anyone know how to do this? Thanks!

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Unfortunately Airtable won’t let you build an array from scratch. All of the array-based functions only work on arrays built by other fields, primarily Rollup and Lookup types. For a while this wasn’t clear in the documentation, but the formula reference page actually says this now (I can’t recall exactly when this was added, but I’m fairly certain it wasn’t there earlier this year when I first began dabbling with Airtable):

“Note that array functions can only be used in rollup fields, or when the input field is a linked record or lookup.”