Question

I have a dictionary structure that maps an id (integer) into a number (double). The numbers are actually weights of an item.

I am writing a function that will allows me to fetch the id of a given weight (if the weight is found in the dict, else, it will return the id of the next closest (i.e. nearest matching) weight.

This is what I have so far:

def getBucketIdByValue(bucketed_items_dict, value):
    sorted_keys = sorted(bucketed_items_dict.keys())
    threshold = abs(bucketed_items_dict[sorted_keys[-2]] -bucketed_items_dict[sorted_keys[-1]]) # determine gap size between numbers

    # create a small dict containing likely candidates
    temp = dict([(x - value),x] for x in bucketed_items_dict.values() if abs(x - value) <= threshold)
    print 'DEBUG: Deviations list: ', temp.keys()
    smallest_deviation = min(temp.keys()) if value >= 0 else max(temp.keys()) # Not sure about this ?
    smallest_deviation_key = temp[smallest_deviation]
    print 'DEBUG: found bucketed item key:',smallest_deviation_key
    return smallest_deviation_key

I’m not sure the logic is actually correct (esp. where I obtain the smallest deviatioon). In any event, if even the logic is correct, this seems an overly complicated way of doing things. Is there a more elegant/pythonic way of doing this?

Off the top of my head, I think a more pythonic/elegant way would be to do something like passing a custom function to the min function – don’t know if that is possible…

[[Update]]

I am running Python 2.6.5

Answer 1

Try sorting the items by the distance of their weight to your target value:

from operator import itemgetter
distances = ((k, abs(v - value)) for k, v in bucketed_items_dict.items())
return min(distances, key=itemgetter(1))[0]

Or using a lambda function instead of itemgetter:

distances = ((k, abs(v - value)) for k, v in bucketed_items_dict.items())
return min(distances, key=lambda x:x[1])[0]