[R] partially sum variable of a dataframe

[Bert Gunter]

In R "array" would mean a matrix, not a data frame. Also, let's name the
frame "cc" as "c" is the name of a commonly used function, and so should be
avoided as the name for an object. In any case, a straightforward
translation using indexing seems simplest:

sum(cc[cc[,"a"] <= 5.25 & cc[,"a"] >= 3, "b"])

Why pursue complexity when the straightforward approach is transparent?

Bert Gunter
Genentech Nonclinical Statistics


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of markleeds at verizon.net
Sent: Wednesday, November 07, 2007 9:02 AM
To: mdgi at gmx.ch
Cc: r-help at r-project.org
Subject: Re: [R] partially sum variable of a dataframe

There's probably a shorter way but below works
and doesn't require the starting points to be in
the a column.

startindex<-3
endindex<-5.25

start<-tail(which(c$a<=startindex),1)
end<-tail(which(c$a<=endindex),1)

sum(c$b[start:end])


>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
>-- 
>Psssst! Schon vom neuen GMX MultiMessenger gehört?
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