How to concatenate elements from a list with another nested list?

Question

I'm trying to concatenate a list with a nested list, but without using dictionary because the dictionary is not keeping the same order and this is screwing a bit what I'm doing. Not sure if this is possible, but basically what I have is:

list1=['a','b','c','d','e']
list2=[['1','2','3'],['4','5','6'],['7','8','9'],['T1','T2','T3'],[]]

and the output I need is:

[['a_1','a_2','a_3'],['b_4','b_5','b_6'],['c_7','c_8','c_9'],['d_T1','d_T2','d_T3'],['e']]

I'm able to do it with a dictionary with this code:

dict = dict(zip(list1, list2))
for key,values in dict.iteritems():
    vals = dict[key]
    values = [key + '_' + str(v) for v in vals]
    test.append(values)

but the order is not the same, and I need to match some lists together later... So I really would prefer to avoid the dictionary part, anyone having any idea?

Thanks!

hiro protagonist · Accepted Answer · 2019-06-03 10:49:33Z

2

you were almost there:

test = []
for key, values in zip(list1, list2):
    if values:
        values = [key + "_" + str(v) for v in values]
        test.append(values)
    else:
        test.append([key])
print(test)

just iterate over the pairs from zip; if you pack that in a dict first it will mess up the order in python 2 (in python >= 3.4 you are fine!).

you could also pack all that directly in a list comprehension (and maybe use string formatting):

test = [
    ["{}_{}".format(key, v) for v in values] if values else [key]
    for key, values in zip(list1, list2)
]

answered Jun 3, 2019 at 10:49

hiro protagonist

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