R：绘制3D交互模型和使用Plotly进行的观察

Question

I start from a simple interaction model z = 0.5*x*y . The goal is to plot simulated observations with add_markers() as well as the model with add_surface() using the plotly library.

So far I have manage to simulate the data and plot it:

library(plotly)
library(magrittr)

x <- rnorm(10000)
y <- rnorm(10000)
z <- 0.5 * x * y

plot_ly() %>% add_markers(x = x, y = y, z = z, marker = list(size = 1))

This is what the plot looks like:

I then tried to surface plot the model:

plot_ly() %>% 
   add_markers(x = x, y = y, z = z, marker = list(size = 1)) %>%
   add_surface(z = matrix(z, 100, 100))

But it produces something completely different to what it would be expected. This is approximately the result that would be expect from the surface plot:

What am I doing wrong?

Answer 1

An easy workaround is to use:

plot_ly(x = x, y = y, z= z, type = 'mesh3d') 

Or using surface plot:

  library(tidyverse)
  grid <- expand.grid(x = seq(from = -3, to = 3, length.out = 100),
                      y = seq(from = -3, to = 3, length.out = 100))

  grid %>%
    mutate(z = 0.5 * x * y) %>%
    spread(key = y, value = z) %>%
    as.matrix() -> z


  plot_ly() %>%
    add_surface(z = z, x = unique(grid$x), y = unique(grid$y)) %>%
    layout(scene = list(xaxis = list(range = c(-2.5, 2.5)),
                        yaxis = list(range = c(-2.5, 2.5)))) #odd artifact if all values are plotted - check without layout call

or:

model = lm(z ~ x * y)

grid <- expand.grid(x = seq(from = -3, to = 3, length.out = 100),
                      y = seq(from = -3, to = 3, length.out = 100))

grid$z = predict(model, grid)

and proceed as above

 grid %>%       
    spread(key = y, value = z) %>%
    as.matrix() -> z