For the purpose of demonstration, we will use an iris flower dataset, which is readily available in R. The iris flower has three different species: iris setosa, iris virginica, and iris versicolor. Fifty samples from each species were collected and, for each sample, four variables were measured: the length and width of the sepals and petals. The name of each flower is stored under the species column, and the length and width of sepal is stored under the Sepal.Length and Sepal.Width columns, respectively. Similarly, the length and width of the petal are stored under the Petal.Length and Petal.Width columns, respectively. The following command shows the first few rows from the iris data frame:
> head(iris) Sepal.Length Sepal.Width Petal.Length Petal.Width Species 1 5.1 3.5 1.4 0.2 setosa 2 4.9 3.0 1.4 0.2 setosa 3 4.7 3.2 1.3 0.2 setosa 4 ...