[Python] How to concatenate nested items in dictionary?

I have a nested dictionary and I want to concatenate the items of the nested dictionaries:

import random
nested_dict = {
k: {
'val0': random.sample(range(100), 2),
'val1': random.sample(range(100), 2),
}
for k in 'abcd'
}


I can make it with a double-loop like this:

from collections import defaultdict

dp_dict= defaultdict(list)

for v in nested_dict.values():
for k, v_nested in v.items():
dp_dict[k].append(v_nested)
val0 = dp_dict['val0']
val1 = dp_dict['val1']


is there a more Pythonic/elegant way to do it?

NB
one solution is to use Pandas, however, this solution is quite ineficcient (X300 slower)

import pandas as pd
val0, val1 = pd.DataFrame(nested_dict).loc[['val0', 'val1']].values

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