[R] Assigning values to several consecutives rows in a sequence while leaving some empty
Berend Hasselman
bhh at xs4all.nl
Mon Oct 22 10:45:31 CEST 2012
On 22-10-2012, at 06:39, nymphita wrote:
> Hello all,
> I'm trying to group several consecutives rows (and assigning them the same
> value) while leaving some of the rows empty (when a certain condition is not
> fulfilled).
>
> My data are locations (xy coordinates), the date/time at which they were
> measured, and the time span between measures. Somehow simplified, they look
> like this:
>
> <http://r.789695.n4.nabble.com/file/n4646956/image1.png>
>
> I'd like to assign a value to every sequence of locations that are measured
> within a time span of 4 hours, and make my data look like this:
>
> <http://r.789695.n4.nabble.com/file/n4646956/image2.png>
>
It's better if you insert the data in the mail using dput().
Nobody wants to enter data from an image.
Generate your data (partially)
Span <- c(NA,4,8,4,4,8,4,8,16,4,4,12)
sqnc <- ifelse(Span<=4,1,0)
Span
sqnc
# step by step
y1 <- diff(sqnc)
y2 <- cumsum(c(1,pmax(y1[-1],0)))
# print
y1
y2
# And this seems to give your desired result
Sequence <- ifelse(sqnc==1,c(0,y2),NA)
Sequence
You could substitute y1 in the expression for y2 and then substitute in the Sequence expression to make the computation more compact.
Berend
> I've tried several algorithms with a loop "for" plus "ifelse" condition
> like:
>
> Sequence <- for (i in 1:max(ID)) {
> ifelse (Span <= 4, i+1, "NA")
> }
>
> without any luck. I know my attempt is incorrect, but my programming skills
> are really basic and I haven't found any similar problem in the web.
>
> Any ideas would be very appreciated!
>
>
>
> --
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>
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