R: Plot Axis Display Values Larger than the Original Data

问题

I am using the R programming language. I am following a tutorial on data visualization over here: https://plotly.com/r/3d-surface-plots/

I created my own data and made a 3D plot:

library(plotly)

set.seed(123)

#generate data
a = rnorm(100,10,10)
b = rnorm(100,5,5)
c = rnorm(100,5,10)
d = data.frame(a,b,c)

#3d plot
fig <- plot_ly(z = ~as.matrix(d))
fig <- fig %>% add_surface()

#view plot
fig

As seen here, there is a point on this 3D plot where "y = 97". I am not sure how this is possible, seeing how none of the values within the original data frame "d" are anywhere close to 97. I made sure of this by looking at the individual distributions of each variable in the original data frame "d":

#plot individual densities 

plot(density(d$a), main = "density plots", col = "red")
lines(density(d$b), col = "blue")
lines(density(d$c), col = "green")

legend( "topleft", c("a", "b", "c"), 
text.col=c("red", "blue", "green") )

As seen here, none of the variables (a,b,c) from the original data frame "d" have any values that are close to 97.

Thus, my question: can someone please explain how is it possible that the point (x = 0 , y = 97, z =25.326) appears on this 3D plot?

Thanks

回答1:

I am not sure if this will resolve the problem - but using the same logic from this previous stackoverflow post: 3D Surface with Plot_ly in r, with x,y,z coordinates

library(plotly)
set.seed(123)

#generate data
a = rnorm(100,10,10)
b = rnorm(100,5,5)
c = rnorm(100,5,10)
d = data.frame(a,b,c)


data = d

plot_ly() %>% 
  add_trace(data = data,  x=data$a, y=data$b, z=data$c, type="mesh3d" )

Now, it appears that all values seen in this visual plot are contained in the original data frame.

However, I am still not sure what is the fundamental (and mathematical) difference between both of these plots:

I am curious to see what others have to say.

Thanks

回答2:

The problem is how you have your matrix built. Basically, the z-values (in your case the c variable) should be given in a matrix in which the rows and columns are like coordinates for a surface, similar to a grid or raster dataset. The values you see now along the x and y-axis are not the values from your a and b variables but the row and column numbers from your matrix (similar to coordinates). You can open the volcano dataset in R and have a look at how these data are organized, which will surely give you a better understanding of what I am trying to explain.

来源：https://stackoverflow.com/questions/65996674/r-plot-axis-display-values-larger-than-the-original-data

标签

plotly

data-visualization