Making a dictionary from a list of strings (creating keys from the elements of the list)

Question

I am using Python 3.3. I was curious how I can make a dictionary out of a list:

Lets say my list containing strings is

list = ['a;alex', 'a;allison', 'b;beta', 'b;barney', 'd;doda', 'd;dolly']

I want to make it into a dictionary like this:

new_dict = { {'a': {'alex','allison'}}
             {'b': {'beta','barney'}}
             {'d': {'doda', 'dolly'}} }

so later I can print it out like this:

Names to be organized and printed:
   a -> {'alex', 'allison'}
   b -> {'beta', 'barney'}
   d -> {'doda', 'dolly'}

How would I approach this? Many thanks in advance!

-UPDATE-

So far I have this:

reached_nodes = {}

for i in list:
    index = list.index(i)
    reached_nodes.update({list[index][0]: list[index]})

But it outputs into the console as:

{'a': 'a;allison', 'b': 'b;barney', 'd': 'd;dolly'}

Have you tried anything so far? If so, can you provide your code? — Ffisegydd, Jan 21 '14 at 07:36
what exactly do you need? is the problem extracting key-value from a string? insert entry to dict? — idanshmu, Jan 21 '14 at 07:39
pretty much a dupe of: http://stackoverflow.com/questions/5378231/python-list-to-dictionary-multiple-values-per-key?rq=1 — some1, Jan 21 '14 at 07:41

Games Brainiac · Accepted Answer · 2014-01-21T07:47:26.150

5

Well, you can use defaultdict:

>>> from collections import defaultdict
>>> l = ['a;alex', 'a;allison', 'b;beta', 'b;barney', 'd;doda', 'd;dolly']
>>> var = defaultdict(list)
>>> for it in l:
    a, b = it.split(';')
    var[a].append(b)
>>> var
defaultdict(<type 'list'>, {'a': ['alex', 'allison'], 'b': ['beta', 'barney'], 'd': ['doda', 'dolly']})
>>> for key, item in var.items():
...     print "{} -> {{{}}}".format(key, item)
...     
a -> {['alex', 'allison']}
b -> {['beta', 'barney']}
d -> {['doda', 'dolly']}

If you would like to get rid of the [], then try the following:

>>> for key, value in var.items():
...     print "{} -> {{{}}}".format(key, ", ".join(value))
a -> {alex, allison}
b -> {beta, barney}
d -> {doda, dolly}

If you would like the values in a set and not a list, then just do the following:

var = defaultdict(set)

And use .add instead of .append.

edited Jan 21 '14 at 07:47

answered Jan 21 '14 at 07:40

Games Brainiac

80,178
33
141
199

@Ffisegydd That can be easily arranged. – Games Brainiac Jan 21 '14 at 07:47
@Ffisegydd Done. Hope that suffices, but I don't think the OP has mentioned his/her exact needs, so I went with list instead of set. – Games Brainiac Jan 21 '14 at 07:49
Of course, +1 :D It was just on the off chance that the OP really did need a set for some reason. – Ffisegydd Jan 21 '14 at 07:51
Thank you! It works. But do is there any chance to forcefully print them out alphabetically? – user2559679 Jan 21 '14 at 08:04
Just run over the dict and sort each list. – Matthias Jan 21 '14 at 08:08
@user2559679 Yea, you can do that easily do that by sorting each list, so before printing `value`, you can just sort it, with `value.sort()`. – Games Brainiac Jan 21 '14 at 08:09
Oh, sorry for being unclear. I'd like to forcefully sort the keys alphabetically. Sometimes I get a, b, d. Other times I get b, d, a. – user2559679 Jan 21 '14 at 08:13
@user2559679 How about you make a separate question, that way you can explain what you want better. Comments are problematic. – Games Brainiac Jan 21 '14 at 08:15
I'm sorry. I will keep that in mind next time. I got it. I sorted the keys alphabetically by sorted(var.items()) before printing. Many thanks! – user2559679 Jan 21 '14 at 08:21

Making a dictionary from a list of strings (creating keys from the elements of the list)

1 Answers1