How To Sort A Dictionary By Two Elements, Reversing Only One

Consider the following dictionary: data = {'A':{'total':3}, 'B':{'total':5}, 'C':{'total':0}, 'D':{'total':0}, } The desired order for above is B, A

Solution 1:

Sort on negative total, that'll reverse put the totals in reverse order without having to use reverse=True. Ties are then broken on the key in forward order:

sorted(data, key=lambda x: (-data[x]['total'], x))

Demo:

>>>data = {'A':{'total':3},...'B':{'total':5},...'C':{'total':0},...'D':{'total':0},...       }>>>sorted(data, key=lambda x: (-data[x]['total'], x))
['B', 'A', 'C', 'D']

This trick only works for numeric components in a sort key; if you have multiple keys that require a sort direction change that are not numeric, you'd have to do a multi-pass sort (sort multiple times, from last key to first):

# when you can't take advantage of numerical values to reverse on# you need to sort repeatedly from last key to first.# Here, sort forward by dict key, then in reverse by totalbykey = sorted(data)
final = sorted(bykey, key=lambda x: data[x]['total'], reverse=True)

This works because the Python sort algorithm is stable; two elements keep their relative positions if the current sort key result is equal for those two elements.