如何从特定的SUBKEY中找到最低正值的顶级KEY？

Question

My data looks like this:

{   
    'test1462477941.log': {   'end_diff': 537,
                               'file_epoch': 1462477941,
                               'start_diff': -33},
    'test1462478161.log': {   'end_diff': 317,
                               'file_epoch': 1462478161,
                               'start_diff': 284},
    'test1462478346.log': {   'end_diff': 132,
                               'file_epoch': 1462478346,
                               'start_diff': 99},
}

What I want to do is find the lowest, positive "start_diff" value in any of the keys and print the relative top level key (the filename). The data structure is throwing me off a bit though.

If using the data above, it shoud find and print out:

test1462478346.log

Is there an elegant way to do this? If not, I'll take anything

Answer 1

Use filter for removing non positive and min with key for search:

a = {
    'test1462477941.log': {'end_diff': 537,
                           'file_epoch': 1462477941,
                           'start_diff': -33},
    'test1462478161.log': {'end_diff': 317,
                           'file_epoch': 1462478161,
                           'start_diff': 284},
    'test1462478346.log': {'end_diff': 132,
                           'file_epoch': 1462478346,
                           'start_diff': 99},
}

only_positive_start_diff = filter(lambda x: x[1]['start_diff'] > 0, a.items())
min_start_diff = min(only_positive_start_diff, key=lambda x: x[1]['start_diff'])

print min_start_diff[0]  # Min log file

Without lambda it's look like:

def only_positive(x):
    return x[1]['start_diff'] > 0

def min_start(x):
    return x[1]['start_diff']

only_positive_start_diff = filter(only_positive, a.items())
min_start_diff = min(only_positive_start_diff, key=min_start)

print min_start_diff[0]

Answer 2

This is a solution using built-in function reduce :

import sys
filename, start_diff = reduce(
    lambda curMin, item:
        curMin if item[1]['start_diff']<0 or item[1]['start_diff']>curMin[1] else (item[0], item[1]['start_diff']),
    inputDict.iteritems(),
    ('not_found.log', sys.maxint))

print filename

Please note that the code is written with Python 2.7. If you use Python 3.x, then you should find reduce function in functools , and dict.iteritems() has been changed to dict.items() .