A data sample is called qualitative, also known as categorical, if its values belong to a collection of known defined non-overlapping classes. Common examples include student letter grade (A, B, C, D or F), commercial bond rating (AAA, AAB, ...) and consumer clothing shoe sizes (1, 2, 3, ...).
The tutorials in this section are based on an R built-in data frame named painters. It is a compilation of technical information of a few eighteenth century classical painters. The data set belongs to the MASS package, and has to be pre-loaded into the R workspace prior to its use.
Composition Drawing Colour Expression School
Da Udine 10 8 16 3 A
Da Vinci 15 16 4 14 A
Del Piombo 8 13 16 7 A
Del Sarto 12 16 9 8 A
Fr. Penni 0 15 8 0 A
Guilio Romano 15 16 4 14 A
The last School column contains the information of school classification of the painters. The schools are named as A, B, ..., etc, and the School variable is qualitative.
 A A A A A A A A A A B B B B B B C C C C C C D D D D
 D D D D D D E E E E E E E F F F F G G G G G G G H H
 H H
Levels: A B C D E F G H
For further details of the painters data set, please consult the R documentation.