From: papagenic <nabble_at_dejademain.com>

Date: Wed, 23 Jan 2008 13:39:06 -0800 (PST)

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Date: Wed, 23 Jan 2008 13:39:06 -0800 (PST)

hello,

I tried your suggestion ,but the first line :
z <- outer(x, x, "-")

seems to fail pretty quickly as the length of the x vector increases. This
is probably because it has to create a matrix of dimension dim(x)*dim(x). I
am wondering if that can be quicker than a building a loop.

Benilton Carvalho wrote:

*>
*

> i'm not so sure i understood, but you might want something in the

*> lines of:
**>
**> z <- outer(x, x, "-")
**> (abs(z)>step)*outer(1:length(x), 1:length(x))*z
**>
**> (not tested)
**>
**> b
**>
**>
**> On Jan 23, 2008, at 11:32 AM, papagenic wrote:
**>
*

>> >> dear experts, >> >> I am new to R and am trying to compute a vector y from a vector x >> where : >> y[i] = sign(x[j]-x[i])*(j-i) with j the first index after i where >> abs(x[j]-x[i]) > to a given step >> y[i] is 0 if there is no such j >> >> I can write this in R as follows >> for(i in 1:length(x)) { >> y[i]=0 >> for(j in i:length(x)) { >> if (abs(x[j]-x[i]) > step) { >> y[i]=sign(x[j]-x[i])*(j-i) >> break; >> } >> } >> } >> >> but I wonder if there is a more efficient way to write this. I >> understand >> explicit looping can often be avoided in R using vector notation. >> >> Thanks for your help >> -- >> View this message in context: >> http://www.nabble.com/newbie%3Alooking-for-an-efficient-way-to-compute-distance-vector-tp15045583p15045583.html >> Sent from the R help mailing list archive at Nabble.com. >> >> ______________________________________________ >> R-help_at_r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code.

> R-help@r-project.org mailing list

-- View this message in context: http://www.nabble.com/newbie%3Alooking-for-an-efficient-way-to-compute-distance-vector-tp15045583p15053174.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Wed 23 Jan 2008 - 21:46:36 GMT

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