Python Nested List manipulation

Question

Hello all python developers, I was playing with python lists and Pandas library and am having a trouble in a list manipulation tasks. I want to merge all test_list[i][0] dictionary items into one nested list index, according to same state name at index 0 of each nested list.

Sample Input:

test_list= [['Alabama', {'Baldwin County': 182265}],
 ['Alabama', {'Barbour County': 27457}],
 ['Arkansas', {'Newton County': 8330}],
 ['Arkansas', {'Perry County': 10445}],
 ['Arkansas', {'Phillips County': 21757}],
 ['California', {'Madera County': 150865}],
 ['California', {'Marin County': 252409}],
 ['Colorado', {'Adams County': 441603}],
 ['Colorado', {'Alamosa County': 15445}],
 ['Colorado', {'Arapahoe County': 572003}]
]

Sample Output:

test_list1= [['Alabama', {'Baldwin County': 182265, 'Barbour County': 27457}],
 ['Arkansas', {'Newton County': 8330, 'Perry County': 10445, 'Phillips County': 21757}],
 ['California', {'Madera County': 150865, 'Marin County': 252409}],
 ['Colorado', {'Adams County': 441603, 'Alamosa County': 15445, 'Arapahoe County': 572003}]
]

I have tried many approaches to solve this but no success so far.I am a beginner python developer. Thanks for helping in advance.

second sample input you mean expected output? that you want to make your list looke like? — Jjj
– Jjj, Commented Oct 30, 2019 at 7:04

Raymond Hettinger · Accepted Answer · 2019-10-30 07:05:35Z

3

Approach

Use collections.defaultdict as a way to group data by a common field (in this case, by state).
For each state, the defaultdict creates a new dict which is updated with the dict.update() method.
Turn the result back into a list with list applied to the dictionary's items (key/value pairs).

Working code

>>> from pprint import pprint
>>> from collections import defaultdict
>>> d = defaultdict(dict)
>>> for state, info in test_list:
        d[state].update(info)

>>> result = list(d.items())
>>> pprint(result)
[('Alabama', {'Baldwin County': 182265, 'Barbour County': 27457}),
 ('Arkansas',
  {'Newton County': 8330, 'Perry County': 10445, 'Phillips County': 21757}),
 ('California', {'Madera County': 150865, 'Marin County': 252409}),
 ('Colorado',
  {'Adams County': 441603, 'Alamosa County': 15445, 'Arapahoe County': 572003})]

answered Oct 30, 2019 at 7:05

Raymond Hettinger

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2 Comments

Furqan Asghar Over a year ago

Thanks a lot for quick respond @raymond-hettinger. Your solution worked efficiently . :)

Aivar Paalberg Over a year ago

If list of lists needed (instead of list of tuples) then result could be written as [[*pair] for pair in d.items()]

wailinux · Accepted Answer · 2019-10-30 07:37:34Z

2

Python3.5 or later

tmp_dict = {}
for lst in test_list:
city = lst[0]
country = lst[1]
if city in tmp_dict:
    tmp_dict[city] = {**tmp_dict[city], **country}
else:
    tmp_dict[city] = country
print(tmp_dict) #you will get dict result
#If you want to get list only
output_result = []
for k in tmp_dict:
    tmp_list.append([k,tmp_dict[k]])
print(output_result) #you will get list result

answered Oct 30, 2019 at 7:37

wailinux

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Python Nested List manipulation

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Working code

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2 Answers 2

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Python3.5 or later

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