Question

I’m trying to define a function that will allow me to get a value count at various levels of a dict. For example, if I have something like:

vehicles = {
    'Ford': {
        'Falcon': {
            '2008': 10, 
            '2009': 12, 
            '2010': 5
        }
    }, 
    'Holden': {
        'Commodore': {
            '2008': 15, 
            '2009': 11, 
            '2010': 5
        }
    }
}

I’d like to be able to call a function that will calculate the values at each depth. So at depth 0, the function would return the sum of every value (58). At depth 1, the function would return a dict with {'Ford': 27, 'Holden': 31}. At depth 2, the function would return a dict with {'Ford': {'Falcon': 27}, 'Holden': {'Commodore': 31}}. Etc…

I think I need to burrow to the max depth and start summing the values as I move back up the levels, but I’m fairly new to Python and I’m struggling. Possibly I would need to use recursion?

Thanks for your help.

Answer 1

My solution, not thoroughly tested

def sum_values(data):
    if type(data.values()[0]) != dict:
        return sum(data.values())
    else:
        return sum(sum_values(v) for v in data.values())

def depth_values(data, depth = 0):
    if depth == 0:
        return sum_values(data)
    else:
        return dict(
            (k, depth_values(v, depth-1))
            for k, v in data.items()
        )

TEST:

print depth_values(vehicles, 0) # >> 58
print depth_values(vehicles, 1) # >> {'Holden': 31, 'Ford': 27}
print depth_values(vehicles, 2) # >> {'Holden': {'Commodore': 31}, 'Ford': {'Falcon': 27}}
print depth_values(vehicles, 3) # exceptions