在我们创建树(iTrees)的部分中,我不明白为什么我们使用以下分类代码行(与决策树分类非常相似):
def classify_data(data):
label_column = data.values[:, -1]
unique_classes, counts_unique_classes = np.unique(label_column, return_counts=True)
index = counts_unique_classes.argmax()
classification = unique_classes[index]
return classification
我们正在选择最后一列和最大唯一元素的索引值?这可能对决策树有意义,但我不明白为什么我们在隔离林中使用它?
整个 iTree 代码如下所示:
def isolation_tree(data,counter=0,
max_depth=50,random_subspace=False):
# End loop if max depth or if isolated
if (counter == max_depth) or data.shape[0]<=1:
classification = classify_data(data)
return classification
else:
# Counter
counter +=1
# Select random feature
split_column = select_feature(data)
# Select random value
split_value = select_value(data,split_column)
# Split data
data_below, data_above = split_data(data,split_column,split_value)
# instantiate sub-tree
question = "{} <= {}".format(split_column,split_value)
sub_tree = {question: []}
# Recursive part
below_answer = isolation_tree(data_below,counter,max_depth=max_depth)
above_answer = isolation_tree(data_above,counter,max_depth=max_depth)
if below_answer == above_answer:
sub_tree = below_answer
else:
sub_tree[question].append(below_answer)
sub_tree[question].append(above_answer)
return sub_tree
编辑:这是数据和运行分类数据的示例:
feat1 feat2
0 3.300000 3.300000
1 -0.519349 0.353008
2 -0.269108 -0.909188
3 -1.887810 -0.555841
4 -0.711432 0.927116
label columns: [ 3.3 0.3530081 -0.90918776 -0.55584138
0.92711613]
unique_classes, counts unique classes: [-0.90918776 -0.55584138
0.3530081 0.92711613 3.3 ] [1 1 1 1 1]
-0.9091877609469025