Fromun- +‎concatenate.

unconcatenate (notcomparable)

1. Notconcatenate.

unconcatenate (third-person singular simple presentunconcatenates,present participleunconcatenating,simple past and past participleunconcatenated)

1. (programming,transitive) To undo the process of concatenation.
   • 2001, Patrick G. McKeown, Craig A. Piercy,Learning to Program with Visual Basic, page181:

     However, since we are going to save this combo box back to the file, this would require “unconcatenating” the names before writing them to file, something we would like to avoid.

   • 2014, Larry Pace,R Recipes: A Problem-Solution Approach, page65:

     The collapse argument tells R to “unconcatenate” the individual lines and create a single string vector.