Consider the 'Diamond' dataset. It is provided as Microsoft Excel Workbook. Data are for 308 round-cut diamonds, taken from a newspaper ad. The codes are as follows:

1. IDNO - an identification number for each data point.

2. WEIGHT - weight of the diamond, in carats.

3. COLOR - degree of colour purity in the diamond: "D" represents top colour purity grade; Lesser grades are "E", "F", and so on, through the alphabet. Note that these grades are ranked and should be coded according to their order.

4. CLARITY - diamond clarity (presence or absence of minute flaws): "IF" means "internally flawless" - the top grade; "VVS1" and "VVS2" for "very very slightly imperfect"; and, "VS1" and "VS2" for "very slightly imperfect". Note that these grades are ranked and should be coded according to their order.

5. RATER - the diamond was evaluated by one of three independent rating agencies: "GIA" - Gemmological Institute of America (based in New York); "IGI" - International Gemmological Institute (Antwerp); "HRD" - Hoge Raad Voor Diamant (Antwerp).

6. PRICE - in Singapore dollars.