CODEWITHSUNDEEP
rdataframeplotcoordinates
user9511625
user9511625

Reputation:

Plotting 2 out of 3 columns of a data frame

I have a data frame consisting of 400 rows of x, y and z values, and I would like to plot the x column against the y column.

This is what I have got so far:

sample3d = function(n)
{
  df = data.frame()
  while(n>0)
  {
    X = runif(1,-1,1)
    Y = runif(1,-1,1)
    Z = runif(1,-1,1)
    a = X^2 + Y^2 + Z^2 
    if( a < 1 )
    {
      b = (X^2+Y^2+Z^2)^(0.5)
      vector = data.frame(X = X/b, Y = Y/b, Z = Z/b) 
      df = rbind(vector,df)
      n = n- 1
    }
  }
  df
}
sample3d(400)

Upvotes: 1

Views: 708

Answers (2)

nicola
nicola

Reputation: 24480

If you need to draw random points on the surface of a sphere, you need just to extract the polar coordinates. Something like that:

sample3d_v2 <- function(n) {
   phi<-runif(n,0,2*pi)
   cost<-runif(n,-1,1)
   sint<-sqrt(1-cost^2)
   data.frame(X=sint*cos(phi),Y=sint*sin(phi),Z=cost)
}

Just some tests:

system.time(old<-sample3d(4000))
#   user  system elapsed 
#  3.895   0.000   3.879
system.time(new<-sample3d_v2(4000))
#   user  system elapsed 
#  0.000   0.000   0.002

As you can see, a gain of thousands of times. Test the results are correct:

require(rgl)
plot3d(old)
open3d();plot3d(new)

Regarding your question: just name the object resulting for your function and plot the X and Y components.

data<-sample3d_v2(400)
plot(data$X,data$Y)

Upvotes: 1

Jannik Buhr
Jannik Buhr

Reputation: 1937

I named the dataframe your function creates data (data <- sample3d(400)).

Then, if you need a scatterplot (points at x and y coordinates) of the X and Y column, you can use base R's function plot(). e.g. plot(x = data$X, y = data$Y). If you are like me and don't want to type data$ before every column you can make the columns available to functions as vectors by wrapping everything inside with(data = data, {...}).

If you want to create a scatterplot of all three coordinates, you might want to check out the packages in the following two examples:

library(scatterplot3d)
with(data = data, {
    scatterplot3d(x = X, y = Y, z = Z)
})

library(rgl)
with(data, {
    plot3d(X, Y, Z)
})

Upvotes: 0

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