Outstanding number at head of data collection (7)
I believe the answer is:
notable
'outstanding' is the definition.
(I've seen this before)
'number at head of data collection' is the wordplay.
'number' becomes 'no' (abbreviation for 'number').
'at head of' means one lot of letters go next to another (some letters go in front of others).
'data collection' becomes 'table' (I can't justify this - if you can you should give a lot more credence to this answer).
'no'+'table'='NOTABLE'
Can you help me to learn more?
(Other definitions for notable that I've seen before include "Worthy of attention, significant" , "Star" , "Prominent" , "VIP" , "Celebrated" .)