Question

Working in python I want to extract a dataset with the following structure:

Each item has a unique ID and the unique ID of its parent. Each parent can have one or more children, each of which can have one or more children of its own, to n levels i.e. the data has an upturned tree-like structure. While it has the potential to go on for infinity, in reality a depth of 10 levels is unusual, as is having more than 10 siblings at each level.

For each item in the dataset I want to show show all items for which this item is their parent… and so on until it reaches the bottom of the dataset.

Doing the first two levels is easy, but I’m unsure how to make it efficiently recurs down through the levels.

Any pointers very much appreciated.

Answer 1

you should probably use a defaultdictionary for this:

from collections import defaultdict    

itemdict = defaultdict(list)
for id, parent_id in itemlist:
   itemdict[parent_id].append(id)

then you can recursively print it (with indentation) like

def printitem(id, depth=0):
    print '  '*depth, id
    for child in itemdict[id]:
        printitem(child, depth+1)