Diamond prices

As influenced by the GIA’s “Four Cs”: Color, Cut, Clarity, and Carat (weight).

First, the rubric requires a date, so we’ll ask R for that:

Sys.Date()

## [1] "2026-05-21"

And then load the needed libraries:

suppressMessages(library(plotly))
suppressMessages(library(tidyverse))

Next, we’ll see how many observations are in the diamonds data set:

dim(diamonds)

## [1] 53940    10

That’s a lot of observations, and that many points will muddy the plot. So we’ll look at a random subset consisting of 5% of the data set:

set.seed(8675309)
dsample <- slice_sample(diamonds, n = dim(diamonds)[1] * 0.05)
print.default(paste('Sample observations:', dim(dsample)[1]))

## [1] "Sample observations: 2697"

And generate the plot:

d_plot <- plot_ly(data = dsample, type = 'scatter3d', 
                  mode = 'markers',
                  x = ~carat, y = ~clarity, z = ~price, 
                  color = ~cut,
                  opacity = 0.75, 
                  marker = list(size = 3), 
                  hovertemplate = paste('Price: $', dsample$price, 
                                        '<br>Weight: ', dsample$carat,
                                        '<br>Clarity: ', dsample$clarity,
                                        '<br>Color: ',dsample$color,
                                        sep = ''),
                  legendgrouptitle = list(text = 'Cut', 
                                          font = list(size = 20)
                                          )
)

3D scatter plot of dsample

Kindly review the notes regarding the nature of the scales on the next slide.

The Scales of Diamond Grading:

The industry-standard grading system is that of the Gemological Institute of America.

• Color is rated D through Z inclusive, with body color increasing as we progress through the alphabet: D, E, F are considered colorless; G, H, I, J are gradations of “near colorless”. It is rare for anything lower on the scale to appear in the retail gem trade unless sold specifically as “colored diamonds.”
• Clarity is rated from “Flawless” and “Internally Flawless” (IF) through two levels each of “Very Very Slightly Included” (VVS), “Very Slightly Included” (VS), “Slightly Included” (SI), and three levels of “Included” (I).
• Cut is rated by GIA on a five-step scale of “Poor” to “Excellent”; these data use a slightly different (older) scale which ranks cut from “Poor” to “Ideal”, though still with five steps. The scale in the data may be considered to roughly correspond to the current GIA grades.
• Carat (weight) is self-explanatory. One might remind the reader that one carat is 0.200g, and is not the same as a “karat,” which is measure of gold purity.