Graph recursion horizontal (breadth first) search

Question

I want to traverse across a tree data, mimicked the scenario as self explanatory python script. I am not able to find why the horizontal nodes are not traversed in recursion.

Explanation: The first string is representation of tree in script. The get_childrens method is how I am getting response from database.

"""
                          1
    11               |              12                        |            13
111     112    113   |   121         122              123     |   
                     |             1221 1222                  |

"""

# Do not edit this function in the same format getting data
def get_childrens(i):
    if i==1: return [11,12,13]
    if i==11: return [111,112,113]
    if i==12: return [121,122,123]
    if i==122: return [1221,1222]

def create_tree(nodeid):
    child_users=get_childrens(nodeid)
    if child_users:
        child_users=[user for user in child_users]
    else: 
        return 

    return {
        "data":{
            "type":nodeid
        },
        "children": [create_tree(e) for e in child_users if create_tree(e)] 
    }



if __name__=="__main__":
    import json
    data= create_tree(1) 

    print json.dumps(data , indent=4)
    print "####################### GETTING THIS #####################"
    {
        "data": {
            "type": 1
        },
        "children": [
            {
                "data": {
                    "type": 11
                },
                "children": []
            },
            {
                "data": {
                    "type": 12
                },
                "children": [
                    {
                        "data": {
                            "type": 122
                        },
                        "children": []
                    }
                ]
            }
        ]
    }
    print "###################### EXPECTED THIS #####################"
    print json.dumps({"data":{"value":1},
        "children":[
                    {"data":{"value":11},
                     "children":[
                        {"data":{"value":111},"children":[]},
                        {"data":{"value":112},"children":[]},
                        {"data":{"value":113},"children":[]},
                      ],  
                     },
                    {"data":{"value":12},
                     "children":[
                        {"data":{"value":121},"children":[
                                   {"data":{"value":1221},"children":[]},
                                   {"data":{"value":1222},"children":[]},
                                                          ]},
                        {"data":{"value":122},"children":[]},
                        {"data":{"value":123},"children":[]},
                      ],  
                     },
                    {"data":{"value":13},
                     "children":[

                      ],  
                     }                    
                    ]

     },indent=4)

Alex Martelli · Accepted Answer · 2014-12-30 04:26:48Z

2

With

[create_tree(e) for e in child_users if create_tree(e)]

you're deliberating eliminating any child who does not in turn have children. So for example "data":{"value":1} only ends up with children 11 and 12, which do have some children themselves, but not 13, which doesn't.

I suspect this is faulty logic, and instead you mean something rather more like

[create_tree(e) or e for e in child_users]

answered Dec 30, 2014 at 4:26

Alex Martelli

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Comments

sudhanshu · Accepted Answer · 2014-12-30 04:49:00Z

0

Thanks Alex, returning the data instead of empty solved the problem.

def create_tree(nodeid):
    child_users=get_childrens(nodeid)
    if child_users:
        child_users=[user for user in child_users]
    else: 
        return {
              "data":{

                 "type":nodeid
              },
              "children":  []
            } 

    return {
              "data":{

                 "type":nodeid
              },
              "children":  [create_tree(e) or e for e in child_users]
            }

answered Dec 30, 2014 at 4:49

sudhanshu

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1 Comment

Alex Martelli Over a year ago

I recommend you move this to an edit of your Q -- it's in appropriate as an A. Moreover, if my A helped, it's good practice to upvote and accept it...

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