Select by name, not by number

i = names.index("mean radius")
radius = X[:, i]

Find the position with names.index(...). Do not hard-code a number.

The breast_cancer data holds 30 real measurements for 569 real patients. Selecting the wrong column produces no error. It returns a different real measurement, your analysis continues, and it gives a confident, wrong answer. In research that produces results nobody can reproduce; in a clinical tool, a wrong recommendation about a real person.

The identical operation runs in tech on a (users, items) matrix, to pull one user’s history before making a recommendation.