Question

I want to sort a dictionary of lists, by third item in each list. It’s easy enough sorting a dictionary by value when the value is just a single number or string, but this list thing has me baffled.

Example:

myDict = {'item1': [7, 1, 9], 'item2': [8, 2, 3], 'item3': [9, 3, 11] }

I want to be able to iterate through the dictionary in order of the third value in each list, in this case item2, item1 then item3.

Answer 1

Here is one way to do this:

>>> sorted(myDict.items(), key=lambda e: e[1][2])
[('item2', [8, 2, 3]), ('item1', [7, 1, 9]), ('item3', [9, 3, 11])]

The key argument of the sorted function lets you derive a sorting key for each element of the list.

To iterate over the keys/values in this list, you can use something like:

>>> for key, value in sorted(myDict.items(), key=lambda e: e[1][2]):
...   print key, value
... 
item2 [8, 2, 3]
item1 [7, 1, 9]
item3 [9, 3, 11]