Sorry, this is my first time to post. 

I have a big data set: first colume is date (ex: 2008-2-150, the second is time (10:30:00), and the following columes are variaty measurement data. Every 30 min, I have one data. 

I want to find an effecient way to calculate the hourly, daily, monthly and yearly average, and plot them, and eventually use these average data to do further analysis. 

Thanks!
Jeff  


      
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