=IF(COUNTIF(A1:A8,A11)=0,"No Data",AVERAGE(IF(A1:A8=A11,B1:B8)))
A1:A8 is the dates (note, more work is needed if this is actually date and
time, but if it is just a date, this will work.
A11 is the date you are wanting to average
B1:B8 is the amount
This is an **array** formula, and must be entered with CTRL+Shift+Enter
--
** John C **

"ser1609" wrote:

I've got a dataset with measurements at different time intervals per day.
Most are on the hour, so I could just create daily average for each 24
entries, but many have more (or less) per day. How do I create a daily
average of each group of numbers per day? The data is formatted as column
A=date, column B=amount