We have data created by an external source (i.e. I cannot just change the names used so it works) — the datetime field is named @timestamp and I had an awful time figuring out out how to address that element within a transformation expression.

Just to make sure I wasn’t doing something silly, I created a copy of the data element named without the at symbol. Voila – transformedtimestamp is populated with a datetime element.

I finally figured it out – it appears that I have encountered a JavaScript limitation. Instead of using the dot-notation to access the element, the array subscript method works – not datum.@timestamp in any iteration or with any combination of escapes.