[R] random point in a circle centred in a geographical position
Dear List members I am trying to find a way to generate a random point in a circle centred in a geographical location. So far I have used the following formula (see code below): random_x = original_x + radius*cos(angle) random_y = original_y + radius*sin(angle) where radius is a random number between 0 and the radius of the circle and angle is between 0 and 360 degrees The code bellow works fine however some people argue that this method will produce uneven locations… I really do not understand why. Another option will be to use the “rejection method”: generate points inside a box and reject points that fall outside the circle. However I think this is much complicate… or at least I don’t know how to programme it. So, 1. Is there any package that generates random points in a circle? (I couldn’t find any) 2. Do you think the code bellow produces uneven locations? 3. Any suggestions to programme the “rejection method”? Maybe someone has already used it... Cheers albert #Code random location in a circle # Generate UTM coordinates (original location) x_utm-c(289800) y_utm-c(4603900) coord-as.data.frame(cbind(x_utm,y_utm)) # Generate a random radius with a maximum distance of 1000 meters from the original location. radius-runif(1,0,1000) # Generate a random angle angle-runif(1,0,360) #Generate a random x coordinate x_rdm-coord$x_utm[1]+radius*cos(angle) #Generate a random y coordinate y_rdm-coord$y_utm[1]+radius*sin(angle) result-as.data.frame(cbind(x_rdm,y_rdm, x_utm, y_utm)) # We can calculate the distance between the original and the random location result$dist_m-sqrt(((coord$x_utm-result$x_rdm)^2+(coord$y_utm-result$y_rdm)^2)) result __ R-help@stat.math.ethz.ch 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] adding columns to a table after a loop
Dear list,
I am trying to find the way to add columns to a table
(or a matrix) after a loop. The result of this loop is
an array and I would like to get all the results in a
single table once the loop is finish. I have
reproduced a simplified example below:
a- 1
b - matrix()
while (a = 4) {
+ b-rnorm(10)
+ a- a +1
+ }
# I have tried several methods but without succes so
far.
result - as.data.frame(cbind(b))
result
b
1 -0.03250661
2 -0.59823770
3 1.58120471
4 0.41086546
5 0.78959090
6 1.23587125
7 0.83427190
8 1.09035581
9 0.11331056
10 0.25267231
the result above is not what I am looking for because
it shows only the results from the last operation in
the loop, I would like to obtain something like the
following.
result
b1 b2 b3 b4
1 -0.08420826 -0.0637943 -0.83246201 -1.0902384
2 0.40623009 -2.7940096 1.37664973 1.6023967
3 -1.13850505 1.1660669 -0.95962296 -0.7325098
4 -1.06183391 1.1063677 1.67948677 -1.9875475
5 -0.64431067 -0.4843952 -1.30742858 0.5064134
6 0.56729468 1.0860484 0.07651954 0.4380108
7 0.95036177 -0.5328609 1.28954934 -0.2775614
8 -0.17848223 0.5340379 -0.22613700 1.0179886
9 2.93145454 -1.8639607 -0.25478610 1.6619754
10 1.51942415 -0.2051423 0.09144450 -1.6329481
I hope someone can give me a hand
best regards
a
p5.vert.ukl.yahoo.com uncompressed/chunked Sat Aug 12 13:14:00 GMT 2006
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
[R] Re : adding columns to a table after a loop
Dear Uwe,
Thanks for your answer. I have been trying your suggestion but I haven't been
able to solve my problem as I may have simplified in excess my example. The
real situation is actually much similar to the following:
a-1
b-1
i-1
pvalue-matrix()
while(a=4) {
while(b=10){
pvalue[i]-rnorm(1)
i-i+1
b-b+1
}
a-a+1
}
To get the desired outcome I have tried two things based on your suggestion:
1)
a-1
b-1
i-1
pvalue- matrix(ncol=4, nrow=10)
result- matrix()
while(a=4) {
while(b=10){
pvalue[i]-rnorm(1)
i-i+1
b-b+1
}
result[,a]-pvalue
a-a+1
}
here I get an error message:
Error in [-(`*tmp*`, , a, value = c(1.38661984066808, -0.641565430307799, :
number of items to replace is not a multiple of replacement length
2)
a-1
b-1
i-1
pvalue-matrix(ncol=4, nrow=10)
while(a=4) {
while(b=10){
pvalue[i,a]-rnorm(1)
i-i+1
b-b+1
}
a-a+1
}
here what I get is:
pvalue
[,1] [,2] [,3] [,4]
[1,] -2.18379100 NA NA NA
[2,] -0.90112392 NA NA NA
[3,] -0.91762163 NA NA NA
[4,] 0.54922398 NA NA NA
[5,] 0.95511590 NA NA NA
[6,] 0.08509518 NA NA NA
[7,] -0.92576835 NA NA NA
[8,] 1.62361191 NA NA NA
[9,] 0.02644486 NA NA NA
[10,] 0.32406407 NA NA NA
I do not know what else to try...
best wishes
a
- Message d'origine
De : Uwe Ligges [EMAIL PROTECTED]
À : Albert Picado [EMAIL PROTECTED]
Cc : r-help@stat.math.ethz.ch
Envoyé le : Samedi, 12 Août 2006, 3h57mn 16s
Objet : Re: [R] adding columns to a table after a loop
Albert Picado wrote:
Dear list,
I am trying to find the way to add columns to a table
(or a matrix) after a loop. The result of this loop is
an array and I would like to get all the results in a
single table once the loop is finish. I have
reproduced a simplified example below:
a- 1
b - matrix()
while (a = 4) {
+ b-rnorm(10)
+ a- a +1
+ }
Staying in your example:
a - 1
b - matrix(nrow=10, ncol=4)
while(a = 4){
b[,i] - rnorm(10)
a - a + 1
}
Uwe Ligges
# I have tried several methods but without succes so
far.
result - as.data.frame(cbind(b))
result
b
1 -0.03250661
2 -0.59823770
3 1.58120471
4 0.41086546
5 0.78959090
6 1.23587125
7 0.83427190
8 1.09035581
9 0.11331056
10 0.25267231
the result above is not what I am looking for because
it shows only the results from the last operation in
the loop, I would like to obtain something like the
following.
result
b1 b2 b3 b4
1 -0.08420826 -0.0637943 -0.83246201 -1.0902384
2 0.40623009 -2.7940096 1.37664973 1.6023967
3 -1.13850505 1.1660669 -0.95962296 -0.7325098
4 -1.06183391 1.1063677 1.67948677 -1.9875475
5 -0.64431067 -0.4843952 -1.30742858 0.5064134
6 0.56729468 1.0860484 0.07651954 0.4380108
7 0.95036177 -0.5328609 1.28954934 -0.2775614
8 -0.17848223 0.5340379 -0.22613700 1.0179886
9 2.93145454 -1.8639607 -0.25478610 1.6619754
10 1.51942415 -0.2051423 0.09144450 -1.6329481
I hope someone can give me a hand
best regards
a
p5.vert.ukl.yahoo.com uncompressed/chunked Sat Aug 12 13:14:00 GMT 2006
__
R-help@stat.math.ethz.ch 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@stat.math.ethz.ch 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.
