extract unique list using criteria

[jimrward]

i have 2 columns of data,

col1 :- devicename which can be repeated a number of times
col2 :- username (sometimes blank)

I need to create a 3rd column containing unique devicenames where the username is blank

 

[Robert Mika]

If your data are in columns A and B try this:
=IF(ROWS($C$1:$C1)<=COUNTIF($B$1:$B$20,"="&""),INDEX($A$1:$A$20,SMALL(IF($B$1:$B$20="",ROW($C$1:$C$20)-ROW($E$1)+1),ROWS($C$1:$C1))),"")

copy down