How do you convert a Dictionary to a List?

Question

For example, if the Dictionary is {0:0, 1:0, 2:0} making a list: [0, 0, 0].

If this isn't possible, how do you take the minimum of a dictionary, meaning the dictionary: {0:3, 1:2, 2:1} returning 1?

Solution 1

convert a dictionary to a list is pretty simple, you have 3 flavors for that .keys(), .values() and .items()

>>> test = {1:30,2:20,3:10}
>>> test.keys() # you get the same result with list(test)
[1, 2, 3]
>>> test.values()
[30, 20, 10]
>>> test.items()
[(1, 30), (2, 20), (3, 10)]
>>> 

(in python 3 you would need to call list on those)

finding the maximum or minimum is also easy with the min or max function

>>> min(test.keys()) # is the same as min(test)
1
>>> min(test.values())
10
>>> min(test.items())
(1, 30)
>>> max(test.keys()) # is the same as max(test)
3
>>> max(test.values())
30
>>> max(test.items())
(3, 10)
>>>     

(in python 2, to be efficient, use the .iter* versions of those instead )

the most interesting one is finding the key of min/max value, and min/max got that cover too

>>> max(test.items(),key=lambda x: x[-1])
(1, 30)
>>> min(test.items(),key=lambda x: x[-1])
(3, 10)
>>>     

here you need a key function, which is a function that take one of whatever you give to the main function and return the element(s) (you can also transform it to something else too) for which you wish to compare them.

lambda is a way to define anonymous functions, which save you the need of doing this

>>> def last(x):
        return x[-1] 

>>> min(test.items(),key=last)
(3, 10)
>>> 

Solution 2

You can simply take the minimum with:

min(dic.values())

And convert it to a list with:

list(dic.values())

but since a dictionary is unordered, the order of elements of the resulting list is undefined.

In python-2.7 you do not need to call list(..) simply dic.values() will be sufficient:

dic.values()

Solution 3

>>> a = {0:0, 1:2, 2:4}
>>> a.keys()
[0, 1, 2]
>>> a.values()
[0, 2, 4]

Comments

[Tasos Papastylianou]

yeah, saw that a second later :p

[Tasos Papastylianou]

you are quick! :D

[Copperfield]

i++ is not valid python

[Copperfield]

also, there is no need to assume anything about the keys (or values) other than they can be compared with one another to find min/max, you go to some weird tangent there

[Narusan]

.items() is genius. I didn't know such a thing existed. Thanks!

[Copperfield]

in your example 2, you assume that that the keys are numbers for, actually I don't understand your goal there :-/ In your point 1, why you would assume that? likewise in point 3, and what is the point of point 4?

[Narusan]

The point of point 4? I wasn't sure what he wanted, but if the keys are numbers, one could simply use an array with the index correlating to the key. {0:1, 3:2, 2:3} would mean that the list looks like [1, 3, 2].

[Narusan]

I wasn't quite sure what the questioner wanted, that's why I provided them with 4 options