[R] Sum with Conditions

[jimdare]

Dear R-Users,

I have a huge data set (172,696 rows) that is set out in the following way:

Area | Length | Species | Method | Date | Events	

I want to sum the number of Events if:

Length < 28                                AND
Species is NOT "X" ,"Y", or "Z"       AND
Method is either "1" ,"2", or "3"       AND
Date is between 31/12/08 AND 1/02/09 (i.e. JAN 09) 

Is there an easy way to do this?

Your help is much appreciated.

James  

      
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