ugly loop

Thanks Marc for your help.

The following code is slow and ugly:

count<-0
for(i in 1:nrow(ver))
  for(j in 1:ncol(ver))
    {
    count<-count+1
    x[count]<-pt$x[ver[i,j]]
    y[count]<-pt$y[ver[i,j]]
    z[count]<-pt$z[ver[i,j]]
    }

Please help me make it better.

Thanks!

The following should work:

ver <- matrix(sample(1:16, 16), ncol = 4)
pt <- data.frame(x = sample(1:16, 16), 

+                  y = sample(1:16, 16),
+                  z = sample(1:16, 16))
 

ver

     [,1] [,2] [,3] [,4]
[1,]    8    9    5   13
[2,]   14   16    1   10
[3,]   12    2   11    7
[4,]    6    3    4   15

pt

    x  y  z
1   6 15 15
2   9  2  3
3  11  1  5
4  14  4 10
5  13  7 14
6   1 14  7
7  15 10  4
8  10  5 12
9   4 12  2
10  8  8 13
11 16 11  1
12  7 13  9
13  2 16 11
14  3  9 16
15  5  6  8
16 12  3  6

x <- pt$x[ver]
y <- pt$y[ver]
z <- pt$z[ver]

This doesn't give the same results as my original code -- it scrambles the 
order.

OK I will explain my example.

pts contains the x, y, z coordinates of some 3D points. These points are 
the vertices of 3D triangles.

ver contains the indexes into pts.

each line of ver contains 3 vertices -- they are the corners of a 
triangle. For example, if line 1 of ver is
10 9 7
That means I need to draw a triangle whose coordinates are
pt$x[10],pt$y[10],pt$z[10]
pt$x[9],pt$y[9],pt$z[9]
pt$x[7],pt$y[7],pt$z[7]

Now it should be clear why the ordering is critical.
I am using rgl.triangles() to plot. It requires the x,y,z coordinates in 
the order I gave in my original code.

count<-0
for(i in 1:nrow(ver))

x

y

z

x <- pt$x[t(ver)]
y <- pt$y[t(ver)]
z <- pt$z[t(ver)]

x

y

z