Most recent usage date

[phongski]

Hello,

I have difficulties in returning the latest usage date for an inventory item using data as shown below.

Itemkey Transaction Type Last Used Date
#595 PPO 1/16/2013
#595 MRI 1/16/2013
#595 PPO 1/16/2013
#595 MRI 1/16/2013
#595 VRI 1/18/2013
#595 VRI 1/18/2013
#595 APM 2/6/2013
#595 APM 2/6/2013
#595 SSO 3/27/2013
#595 VRI 1/16/2013
#595 VRI 1/16/2013
#595 MRI 1/18/2013
#595 MRI 1/18/2013

I used following formula but the result did not turn out as expected.

if {INTXDH.Transactiontype} in ["APM" , "AIS", "SSO", "PM"]
then cstr(maximum ({INTXDH.Postdate},{INTXDH.Itemkey})) else
"No Usage"

Somehow, my formula only looks at the last record and returns “No Usage” in the example above instead of 03/27/2013. Could someone help me find a solution for this please? Thank you very much in advance for your time and help.

Phongski