# [R] Help with programming a tricky algorithm

arun smartpink111 at yahoo.com
Sun Oct 21 16:36:33 CEST 2012

```HI,
I am not sure whether this is what you want.
idxy    ix    iy    country    col5
1        1    1    c1            x1
2        1    2    c1            x2
3        1    3    c1            x3
4        2    4    c1            x4
5        2    4    c2            x5
6        2    5    c2            x6
7        3    5    c3            x7
8        3    5    c3            x8
9        3    5    c3            x9
country1<-as.numeric(gsub(".*(\\d+)","\\1",Mydata\$country))
Mydata1<-data.frame(ix=abs(diff(c(Mydata\$ix[2],Mydata\$ix))),iy=abs(diff(c(Mydata\$iy[2],Mydata\$iy))),country=abs(diff(c(country1[2],country1))))
Mydata2<- Mydata[apply(Mydata1,1,function(x) all(!duplicated(x)|!duplicated(x,fromLast=TRUE))),]
Mydata2\$border<-1
res<-merge(Mydata,Mydata2,by.x=c("idxy","ix","iy","country","col5"),by.y=c("idxy","ix","iy","country","col5"),all.x=TRUE)
res
#  idxy ix iy country col5 border
#1    1  1  1      c1   x1      1
#2    2  1  2      c1   x2      1
#3    3  1  3      c1   x3      1
#4    4  2  4      c1   x4      1
#5    5  2  4      c2   x5      1
#6    6  2  5      c2   x6      1
#7    7  3  5      c3   x7      1
#8    8  3  5      c3   x8     NA
#9    9  3  5      c3   x9     NA

----- Original Message -----
From: Andrew Crane-Droesch <andrewcd at gmail.com>
To: r-help at r-project.org
Cc:
Sent: Saturday, October 20, 2012 3:36 AM
Subject: [R] Help with programming a tricky algorithm

Hi All,

I'm a little stumped by the following problem.  I've got a dataset with the following structure:

idxy    ix    iy    country    (other variables)
1        1    1    c1            x1
2        1    2    c1            x2
3        1    3    c1            x3
.        .        .       .            .

3739    55    67    c7        x3739
3740    55    68    c7        x3740

where ix and iy are interger-valued indices of the actual x and y coordinates for the gridded data

I want to define a "border" variable that equals 1 if the cell north, east, west, or south of it has a different value of the country variable.  So, for the row with idxy = 1, border would equal 1 if there is any idxy with country !=c1 and ix = 2 (or zero) or iy = 2 (or zero).

Any thoughts?

Thanks!
Andrew

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