[R] partially sum variable of a dataframe

[mdgi at gmx.ch]

Hello,

A stupid question:

I have an array with two columns, the first "a" acting as my index in 0.25 steps, the second one "b" the column of interest. How can i sum up "b" only for a specified window in "a" (as the window command for time series)

a=seq(0,10,0.25)
b=runif(41)
c=data.frame(a,b)

Sum up c if 3<a<5.25

How to do that? thanks

marc
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