Concatenating irregular lists in python dictionaries

Question

I have a python dictionary with 2 lists like below

dict_ans={'Car':[['Toyota', 'Honda'], ['Ford','GM']],
          'Truck':['Kenworth', 'Mack']
         }

I am trying to get it in the format below:

dict_ans={'Car':['Toyota', 'Honda','Ford','GM'],
          'Truck':['Kenworth','Mack']
         }

I tried a few options in the link https://stackabuse.com/python-how-to-flatten-list-of-lists But in each case the 'Truck' resolves to ['K','e','n','w','o','r','t','h','M','a','c','k'] The Car entry worked fine. Any thoughts on the best way to achieve this? Thanks!

You could check the element type prior to flattening. If the list contains lists, flatten, otherwise don't. — Carcigenicate, Jun 24 '21 at 19:17
Include the code you tried _as a part of your question_, not as a link to an external site — Pranav Hosangadi, Jun 24 '21 at 19:17

score 1 · Accepted Answer · answered Jun 24 '21 at 19:22

1

Try dictionary comprehension with numpy.hstack

import numpy as np

new_dict = {k:np.hstack(v).tolist() for k,v in dict_ans.items()} 
# {'Car': ['Toyota', 'Honda', 'Ford', 'GM'], 'Truck': ['Kenworth', 'Mack']}

answered Jun 24 '21 at 19:22

It_is_Chris

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You don't need to rebuild the dict or even rebind the values, since lists are mutable. `for v in dict_ans.values(): v[:] = np.hstack(v)` – wjandrea Jun 24 '21 at 19:28

score 0 · Answer 2 · answered Jun 24 '21 at 19:31

Maybe a custom function and dict comprehension?

def flatten(x):
    if isinstance(x, list):
        return [a for i in x for a in flatten(i)]
    else:
        return [x]
>>> {k: flatten(dict_ans[k]) for k in dict_ans}
{'Car': ['ToyotaHonda', 'Ford', 'GM'], 'Truck': ['Kenworth', 'Mack']}

Concatenating irregular lists in python dictionaries

2 Answers2