Python - Returning a substring of strings within a nested list

Question

I have a nested list of strings:

d =  [['one\\alpha','two\\beta','three\\gamma'],['foo\\data','bar\\params']]

What I want to do is given the list d return a list:

data = [['alpha','beta','gamma'],['data','params']]

That is iterate through each element of the each inner list in d and return the substring after the \\.

My attempt at a solution is:

data = []
for n in range(len(d)):
   for m in range(len(d[n])):
    a = str(d[n][m])
    data.append(a.split("\\")[1])

Which produces: data = ['alpha', 'beta', 'gamma', 'data', 'params']

Which produces the correct strings in the correct sequence, but i lose the nature of how the list d was nested. Is there anyway to produce the list data given d that keeps the nested structure?

Edit:

I've actually just managed to solve this using:

 [[d[n][m].split("\\")[1] for m in range(len(d[n]))] for n in range(len(d))]

Glad you managed to solve it yourself... However, it's not very readable... You hardly ever need to use range over an objects length to loop over it — Jon Clements
– Jon Clements, Commented Oct 26, 2013 at 22:03

Jon Clements · Accepted Answer · 2013-10-26 22:02:24Z

2

You can use a list-comp:

d =  [['one\\alpha','two\\beta','three\\gamma'],['foo\\data','bar\\params']]  
new = [[el.partition('\\')[2] for el in item] for item in d]
# [['alpha', 'beta', 'gamma'], ['data', 'params']]

answered Oct 26, 2013 at 22:02

Jon Clements

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2 Comments

Holtz Over a year ago

Is there any difference between using the partition method and using the split method..?

Jon Clements Over a year ago

Partition only splits once, and will guarantee an empty string for the second split if no separator is found... while when using split, and attempting to take an element, it may throw an IndexError when attemping to access it (eg: 'hello'.split('x')[1] will break) while using partition it won't, it'll just be blank

score 2 · Accepted Answer · 2013-10-26 22:22:56Z

2

Here is my take:

>>> lst = [['one\\alpha','two\\beta','three\\gamma'],['foo\\data','bar\\params']]
>>> [[y.split('\\')[1] for y in x] for x in lst]
[['alpha', 'beta', 'gamma'], ['data', 'params']]
>>>

The important parts of this are a list comprehension and str.split.

edited Oct 26, 2013 at 22:22

answered Oct 26, 2013 at 22:04

user2555451

Comments

Simeon Visser · Accepted Answer · 2013-10-26 21:59:56Z

0

You need to use a list for each of the lists in the input list:

data = []
for n in range(len(d)):
    sublist = []
    for m in range(len(d[n])):
        a = str(d[n][m])
        sublist.append(a.split("\\")[1])
    data.append(sublist)

This gives the desired result:

>>> data
[['alpha', 'beta', 'gamma'], ['data', 'params']]

You can also use a list comprehension to achieve the same result:

data = [[value.split('\\')[1] for value in item] for item in d]

answered Oct 26, 2013 at 21:59

Simeon Visser

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Comments

OdraEncoded · Accepted Answer · 2013-10-26 22:06:01Z

0

List comprehension solution just for the sake of it.

d =  [['one\\alpha','two\\beta','three\\gamma'],['foo\\data','bar\\params']] 
index_to_get = 1

data = [
    list(values[index_to_get]) for values in (
        zip(*(string.split("\\") for string in nested_list))
        for nested_list in d
    )
]

print(data)
>> [['alpha', 'beta', 'gamma'], ['data', 'params']]

answered Oct 26, 2013 at 22:06

OdraEncoded

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