R_User - 5 months ago 55

R Question

I have a 3D dataset:

`data = data.frame(`

x = rep( c(0.1, 0.2, 0.3, 0.4, 0.5), each=5),

y = rep( c(1, 2, 3, 4, 5), 5)

)

data$z = runif(

25,

min = (data$x*data$y - 0.1 * (data$x*data$y)),

max = (data$x*data$y + 0.1 * (data$x*data$y))

)

data

str(data)

And I want to plot it, but the built-in-functions of R alwyas give the error

increasing 'x' and 'y' values expected

`# ### 3D Plots ######################################################`

# built-in function always give the error

# "increasing 'x' and 'y' values expected"

demo(image)

image(x = data$x, y = data$y, z = data$z)

demo(persp)

persp(data$x,data$y,data$z)

contour(data$x,data$y,data$z)

When I searched on the internet, I found that this message happens when combinations of X and Y values are not unique. But here they are unique.

I tried some other libraries and there it works without problems. But I don't like the default style of the plots (the built-in functions should fulfill my expectations).

`# ### 3D Scatterplot ######################################################`

# Nice plots without surface maps?

install.packages("scatterplot3d", dependencies = TRUE)

library(scatterplot3d)

scatterplot3d(x = data$x, y = data$y, z = data$z)

# ### 3D Scatterplot ######################################################

# Only to play around?

install.packages("rgl", dependencies = TRUE)

library(rgl)

plot3d(x = data$x, y = data$y, z = data$z)

lines3d(x = data$x, y = data$y, z = data$z)

surface3d(x = data$x, y = data$y, z = data$z)

Why are my datasets not accepted by the built-in functions?

Thanks for your help,

Sven

Answer

If you're working with "real" data for which the grid intervals and sequence cannot be guaranteed to be increasing or unique (hopefully the `(x,y,z)`

combinations are unique at least, even if these triples are duplicated), I would recommend the `akima`

package for interpolating from an irregular grid to a regular one.

Using your definition of `data`

:

```
library(akima)
im <- with(data,interp(x,y,z))
with(im,image(x,y,z))
```

And this should work not only with `image`

but similar functions as well.

Note that the default grid to which your data is mapped to by `akima::interp`

is defined by 40 equal intervals spanning the range of `x`

and `y`

values:

```
> formals(akima::interp)[c("xo","yo")]
$xo
seq(min(x), max(x), length = 40)
$yo
seq(min(y), max(y), length = 40)
```

But of course, this can be overridden by passing arguments `xo`

and `yo`

to `akima::interp`

.