function that calculate the misclassification error of the subtree stremming from node penalized by alpha
cost_error(node, tree, alpha)
| node | the number of the node in the tree |
|---|---|
| tree | a tree. A data frame returned by the function |
| alpha | a positive real. It is the value of the complexity paramter in the cost-complexity criterion. |
a numeric indicating the misclassification error of the subtree stremming from node penalized by alpha.