[R] only 0s may be mixed with negative subscripts

[ilai]

The function you posted runs without error (on these 6 lines), but
does not return anything that looks remotely like a sum, or cumsum of
anything. Can you clarify what you are trying to do? I assume by "sum
of every other row" you don't mean summing Time, X and Y for rows
1,3,5,..., ?

For the sum of sens2[c(1,3,5,...),] for every column (assuming no NA's
in the data) you could

 (1:nrow(sens2) %% 2) %*% as.matrix(sens2)

           Time       Y         X rownumber
[1,] 3985695201 0.56826 0.1369527         9

Hope this helps


On Mon, Feb 13, 2012 at 11:56 AM, Hasan Diwan <hasan.diwan at gmail.com> wrote:
> I'd like to get the sum of every other row in a data.frame. When I
> actually set about doing this, I get the error in the subject line of
> this message. A sample of my data is below, followed by the function
> call that should give me the results I want:
>
>> dput(head(sens2))
> structure(list(Time = c(1328565067, 1328565067.05, 1328565067.1,
> 1328565067.15, 1328565067.2, 1328565067.25), Y = c(0.0963890795246276,
> 0.227296347215609, 0.240972698811569, 0.221208948983498, 0.230898231782485,
> 0.203282153087549), X = c(0.0245045248243853, 0.0835679411703579,
> 0.0612613120609633, 0.058568910563872, 0.0511868450318788, 0.0557714205674231
> ), rownumber = 1:6), .Names = c("Time", "Y", "X", "rownumber"
> ), row.names = c(NA, 6L), class = "data.frame")
>> speedX <- sapply(sens2[sens2$rownumber %% 2 == 0,], function(row) { cumsum(c(sens2[row+1,3], sens2[row,3]))}, simplify=TRUE)
> Error in xj[i] : only 0's may be mixed with negative subscripts
> Help?
> --
> Sent from my mobile device
> Envoyait de mon portable
>
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