GroupColumns raising exception in v18

[#1]

Dear Community,

Since I moved to v18, a function call that previously worked fine, now raises an exception (in Debug mode only, otherwise, just skipped silently):

• This worked in v17:

colList = dt2 << Get Column Names( String );
dt2 << GroupColumns( colList[1] :: :Time At Exit );

• Raises this exception in v18
  
• FYI, this explicit workaround works:
  

  dt2 << GroupColumns( :Time At Entrance Queue :: :Time At Exit );

Can anyone tell why colList[1] does not work anymore in this context?

[#2 · Accepted solution]

My guess is that JMP18 doesn't like you mixing string with the other format (that format is overall very weird). Personally I would just use list of columns or name of column (as a string) and number. https://www.jmp.com/support/help/en/18.1/#page/jmp/group-columns.shtml#ww805157