如何将键和值从字典连接到列表？

Question

I'm trying to concatenate key and value from a dictionary, and I would like to put them in a sublist according to the key; but I do not succeed. So far what I have (working on Python 2.7):

I managed to concatenate the key and values, but not to split them in different sublists.

dict = {'v1':[1, 2, 3], 'v2': [1, 2, 3, 4]}

concat = []
for key in dict.keys():
    vals = dict [key]
    for v in vals:
        concat.append(str(key + '_' + str(v)))

I get:

 ['v1_1', 'v1_2', 'v1_3', 'v2_1', 'v2_2', 'v2_3', 'v2_4']

but I would like:

[['v1_1', 'v1_2', 'v1_3'], ['v2_1', 'v2_2', 'v2_3', 'v2_4']]

Answer 1

dict = {'v1':[1, 2, 3], 'v2': [1, 2, 3, 4]}
res=[]
for key in dict.keys():
    vals = dict [key]
    res.append([ key+'_'+str(v) for v in vals])

Answer 2

You could use this list comprehension. Python 3.6+.

>>> [[ f'{k}_{x}' for x in dict[k] ] for k in dict]
[['v1_1', 'v1_2', 'v1_3'], ['v2_1', 'v2_2', 'v2_3', 'v2_4']]

Or for Python < 3.6.

>>> [[ '%s_%d' % (k,x)  for x in d[k] ] for k in d]
[['v1_1', 'v1_2', 'v1_3'], ['v2_1', 'v2_2', 'v2_3', 'v2_4']]

Answer 3

You are appending to the same list on both levels of your for loop. Change it to

for key in dict.keys():
    sublist = []
    vals = dict [key]
    for v in vals:
        sublist.append(str(key + '_' + str(v)))
    concat.append(sublist)