how to get seasonal time series?

Wed Nov 29 21:41:56 EST 2006

Hello friends,

Can you tell me how to get seasonal series from a monthly data set? I mean, The variables I have are monthly mean, from 1957.9 to 2002.8.  How can I extract JJA datasets, and get a summer mean time series from 1958 to 2000?

Any suggestion will be appreciated! Thank you !

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