The probabilities p(di |c j ) derive from the distribution of values for each attribute
i, for each class c j . This distribution is computed from the training instances
that belong to each class c j ; the distribution is usually approximated by
a histogram. For instance, we may divide the range of values of attribute i into
equal intervals, and store the fraction of instances of class c j that fall in each
interval. Given a value di for attribute i, the value of p(di |c j) is simply the fraction
of instances belonging to class c j that fall in the interval to which di belongs.