FP-Growth 算法中的递归

Question

I am trying to implement FP-Growth (frequent pattern mining) algorithm in Java. I have built the tree, but have difficulties with conditional FP tree construction; I do not understand what recursive function should do. Given a list of frequent items (in increasing order of frequency counts) - a header, and a tree (list of Node class instances) what steps should the function take?

I have hard time understanding this pseudocode above. Are alpha and Betha nodes in the Tree, and what do generate and construct functions do? I can do FP-Growth by hand, but find the implementation extremely confusing. If that could help, I can share my code for FP-Tree generation. Thanks in advance.

Answer 1

1. alpha is the prefix that lead to this specific prefix tree
2. beta is the new prefix (of the tree to be constructed)
3. the generate line means something like: add to result set the pattern beta with support anItem.support
4. the construct function creates the new patterns from which the new tree is created

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an example of the construct function (bottom up way) would be something like:

function construct(Tree, anItem)   
    conditional_pattern_base = empty list
    in Tree find all nodes with tag = anItem
    for each node found:
       support = node.support
       conditional_pattern = empty list
       while node.parent != root_node
            conditional_pattern.append(node.parent)
            node = node.parent
       conditional_pattern_base.append( (conditional_pattern, support))
    return conditional_pattern_base