extracting columns from a ts series

Hi All,

I have a time series called 'upwelling',  like this:

upwell

        Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov
1984                          494.7 303.7 220.8 288.4 188.1 125.5 215.7
1985    56.0 127.4 165.8 189.4 261.6 223.7 186.3 150.2 107.8 120.3  91.1

from 1984 until 2000. How do I could extract, i.e, Jan or Dec columns from
the data? Or how do I could calculate, say, winter upwelling: Dec+Jan+Feb+Mar?

See ?window

For Dec columns use 
 window(upwell, start=c(1984, 12), frequency=1)
 
Don't know an exact translation for "upwelling" in german, but to sum
over the specified 4 months, you can use:
 sum(window(upwell, start=c(1984, 12), end=c(1985,3)))

Uwe Ligges
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