Match date to project in array and calculate days since last project of same name

I am having trouble with IF and MATCH statements for dates, thinking I might need to use INDEX or VLOOKUP with MIN for this? Basically, I have a worksheet with dates in one columns and i.e. projects in another column. I would like to calculate the average difference in days between matching projects in one column, then the number of days since the last project in another column.

Example:

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I am not trying to calculate time between Project X and Project Y, I am trying to calculate times between projects of the same matching name.

Dates won't be chronological so it will need to match the project to its date, then find the previous projects and their respective dates, and calculate the average number of days between projects of the same name. (There will be more than 2 projects btw, there will be a lot.) So in the example above, for Project X there are an average 733 days before the next Project X because 05/16/2012-07/07/2011=314 and 07/07/2011-05/11/2008=1152, and the average of those two is 733. Project X's most recent occurrence was 5/16/2012, so that was 340 days ago. The most recent Project Y was actually 09/05/2010 so 09/05/2010-03/05/2010=184, and 03/05/2010-11/07/2005=1579....the average of those is 882 (rounded). The number of days since the last Project Y is 959.

Make sense?

If the average days can't be calculated or would be too difficult then I would be happy to at least calculate days since most recent matching project.