On Feb 15, 2011, at 8:22 PM, Peter Alspach wrote:
Tena koe D'Arcy
You might find dist() more suited to your needs.
HTH ....
Peter Alspach
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-bounces@r-
project.org] On Behalf Of Darcy Webber
Sent: Wednesday, 16 February 2011 1:10 p.m.
To: r-help@r-project.org
Subject: [R] distance between consecutive points
Dear R users,
I have two coloumns of data, say x and y, referring to a list of
points in 2D space. I am trying to develop a code that will give me
the distances (using Pythagoras) between consecutive points (xi,yi)
and (xi+1,yi+1). So far I have come up with the following:
for (i in 1:length(x)) d<-sqrt((x[i+1]-x[i])^2+(y[i+1]-y[i])^2)
Or try:
for (i in 1:(length(x)-1) ) d<-sqrt((x[i+1]-x[i])^2+(y[i+1]-y[i])^2)
> d
[1] 0.01
However if you try to generalize this you should to something that
will allow successive values do not get overwritten. Rather than using
d try setting d <- vector("numeric", length(x)-1), the assing to d[i]:
for (i in 1:(length(x)-1) ) d[i]<-sqrt((x[i+1]-x[i])^2+(y[i+1]-y[i])^2)
--
David.
For example, if I use the two points (note, I have hundreds of points
for x,y)
x<-c(64.59,64.60)
y<-c(-179.28,-179.28)
d should be 0.01.
But it just doesn't give me the correct answer and I can't figure out
why. Any help would be much appreciated.
Cheers,
D'Arcy
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