Nested list to nested dictionary in python

Question

I have what seems to be a tricky question, but probably quite a simple solution.

I have a nested list that I wish to have the first value of every list contained to be the key within a dictionary. I wish to have every other element contained within that list to be added as a value to that key.

Here is a sample of the nested list:

stations[[1, 'carnegie', 12345, 30],[2, 'london', 12344, 30], [4, 'berlin', 1345563, 30]]

I wish to convert this to a dictionary in the following format:

stations {1:['carnegie', 12345, 30], 2:['london', 12344, 30], 4:['berlin', 1345563, 30]}

The nested list is quite large, so I've only included as sample here :)

My current attempts have yielded the best option as:

newDict = dict.fromkeys(stations,{})

Which gives me:

{1: {}, 2:{}, 4:{}}

To which I'm at a loss how to combine both the keys and values to make my ideal dictionary.

Any help on this would be great.

EDIT:

To add, I'd like to be able to assign a variable name to the dictionary as with the current solution provided below:

{i[0] : i[1:] for i in stations}

This give me the correct output in a loop, but when I assign a variable to it in the loop it gives me the final key:value in the dictionary

newDict = {}
 for y in stations:
   newDict = {y[0] : y[1:]}

print newDict

returns:

{4: ['berlin', 1345563, 30]}

Thanks!

Cory Kramer · Accepted Answer · 2014-08-30 15:36:22Z

3

>>> stations = [[1, 'carnegie', 12345, 30],[2, 'london', 12344, 30], [4, 'berlin', 1345563, 30]]

You can use a dict comprehension

>>> {i[0] : i[1:] for i in stations}
{1: ['carnegie', 12345, 30], 2: ['london', 12344, 30], 4: ['berlin', 1345563, 30]}

answered Aug 30, 2014 at 15:36

Cory Kramer

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5 Comments

Blckknght Over a year ago

In Python 3, you can use the expanded iterable unpacking syntax to avoid the index and slice, if you want: {key: value for key, *value in stations}

Ben W Over a year ago

This does the job. However when I attempt to assign the results for that loop to a variable it only gives me the last key and it's elements. ie: print newDict returns {4: ['berlin', 1345563, 30]} Is there a way to remedy this?

Jon Clements Over a year ago

@BenW the dict-comp is already a loop - all you're doing in your loop is keep creating a new dictionary with a single entry each turn... Take cyber's code and do: newDict = {i[0] : i[1:] for i in stations} - there ya go... all done...

Ben W Over a year ago

@JonClements + Cyber: Had a bit of trouble with that in Eclipse. Realised even changing to 2.76 as the interpreter and explicitly stating so in numerous places in Eclipse it just wouldn't work. So I tried a restart and now it's all hunky dory. Thanks everyone!

Jon Clements Over a year ago

@BenW don't forget to accept Cyber's answer if it's worked for you

Scorpion_God · Accepted Answer · 2014-08-30 15:37:32Z

1

Use a dict comprehension:

{i[0]: i[1:] for i in stations}

answered Aug 30, 2014 at 15:37

Scorpion_God

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