CODEWITHSUNDEEP
pythonlistdictionary
Tarun K
Tarun K

Reputation: 499

How to do List flattening inside the loop with list comprehension?

here i am having list of dictionaries, my goal is to iterate over list and whenever there is 2 or more list available, i want to merge them and append in a output list, and whenever there is only one list it needs to be stored as it as.

data = [
            [[{'font-weight': '1'},{'font-weight': '1'}],[{'font-weight': '2'},{'font-weight': '2'}]],
            [{'font-weight': '3'},{'font-weight': '3'},{'font-weight': '3'}],
            [[{'font-weight': '1'},{'font-weight': '1'}],[{'font-weight': '2'},{'font-weight': '2'}]],
            [{'font-weight': '3'},{'font-weight': '3'}]
        ]

I can do list flattening for particular element data[0]

print([item for sublist in data[0] for item in sublist])
[{'font-weight': '1'}, {'font-weight': '1'}, {'font-weight': '2'}, {'font-weight': '2'}]

Expected output :

data = [
            [{'font-weight': '1'},{'font-weight': '1'},{'font-weight': '2'},{'font-weight': '2'}],
            [{'font-weight': '3'},{'font-weight': '3'},{'font-weight': '3'}],
            [{'font-weight': '1'},{'font-weight': '1'},{'font-weight': '2'},{'font-weight': '2'}]
            [{'font-weight': '3'},{'font-weight': '3'}]
        ]

Upvotes: 2

Views: 115

Answers (3)

SuperNova
SuperNova

Reputation: 27466

iterate through list and check if each item is lists of list. If so flatten it.

data = [
         [[{'font-weight': '1'},{'font-weight': '1'}],[{'font-weight': '2'},{'font-weight': '2'}]],
         [{'font-weight': '3'},{'font-weight': '3'},{'font-weight': '3'}],
         [[{'font-weight': '1'},{'font-weight': '1'}],[{'font-weight': '2'},{'font-weight': '2'}]],
         [{'font-weight': '3'},{'font-weight': '3'}]
       ]
for n, each_item in enumerate(data):
   if any(isinstance(el, list) for el in each_item):
        data[n] = sum(each_item, [])

print data

Upvotes: 0

Rahul K P
Rahul K P

Reputation: 16081

Try this,

result = []
for item in data:
    result.append([i for j in item for i in j])

Single line code with list comprehension,

[[i for j in item for i in j] for item in data]

Alternative method,

import numpy as np
[list(np.array(i).flat) for i in data]

Result

[[{'font-weight': '1'},
  {'font-weight': '1'},
  {'font-weight': '2'},
  {'font-weight': '2'}],
 [{'font-weight': '3'}, {'font-weight': '3'}, {'font-weight': '3'}],
 [{'font-weight': '1'},
  {'font-weight': '1'},
  {'font-weight': '2'},
  {'font-weight': '2'}],
 [{'font-weight': '3'}, {'font-weight': '3'}]]

Upvotes: 3

Ami Tavory
Ami Tavory

Reputation: 76297

You could use conditional list comprehension with itertools.chain for those elements which need flattening:

In [54]: import itertools

In [55]: [list(itertools.chain(*l)) if isinstance(l[0], list) else l for l in data]
Out[55]: 
[[{'font-weight': '1'},
  {'font-weight': '1'},
  {'font-weight': '2'},
  {'font-weight': '2'}],
 [{'font-weight': '3'}, {'font-weight': '3'}, {'font-weight': '3'}],
 [{'font-weight': '1'},
  {'font-weight': '1'},
  {'font-weight': '2'},
  {'font-weight': '2'}],
 [{'font-weight': '3'}, {'font-weight': '3'}]]

Upvotes: 5

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