Mapping data flow expression for converting simpledate time format to epoch timestamp

Question

There are existing functions where in we can convert datetime from epoch to other formats. What could be the possible function combination to convert a particular datetime as below to epoch timestamp.

Ex:
lastconnected: "2018-09-21T16:47:53.5633865Z"

converted from above to timestamp as first step using below

toTimestamp(lastconnected,'yyyy-MM-dd\'T\'HH:mm:ss', 'GMT')

but further how to convert it into epoch time. Tried add or subtract days and using the other "secondds" or milliseconds functions, but not working..

need lastconnected in epoch format as output.

Answer 1

toLong(rtrim(toString(toTimestamp(lastconnected,'yyyy-MM-dd\'T\'HH:mm:ss', 'GMT')-toTimestamp('1970-01-01T00:00:00','yyyy-MM-dd\'T\'HH:mm:ss', 'GMT')),'000'))

Got a solution using above method, however wanted to check if there is any other way of doing the same.