Converting list of lists / nested lists to list of lists without nesting

Question

I want to convert my list of lists and within these lists there are list into only list of lists. For example:

My code:

a = [[], [], [['around_the_world']], [['around_the_globe']], [], [], [], []]
aaa = len(a)
aa = [[] for i in range(aaa)]
for i, x in enumerate(a):
    if len(x) != 0:
        for xx in x:
            for xxx in xx:
                aa[i].append(xxx)
print(aa)

Currently:

a = [[], [], [['around_the_world']], [['around_the_globe']], [], [], [], []]

to expected:

[[], [], ['around_the_world'], ['around_the_globe'], [], [], [], []]

My current code works in finding the expected output. However, i have to use too many for loop and its too deep. Is there a shorter way to do so like just in one or 2 lines?

Is there anyone can help me in this?

Beginner
– Beginner

2018-10-05 05:28:23 +00:00
Commented Oct 5, 2018 at 5:28 — Beginner
– Beginner, Commented Oct 5, 2018 at 5:28

benvc · Accepted Answer · 2018-10-05 05:26:33Z

1

You can do it with list comprehension, just by checking to see whether the nested list is empty or not, and, if not, replacing the outer list with the inner list (by index).

data = [[], [], [['around_the_world']], [['around_the_globe']], [], [], [], []]

result = [d[0] if d else d for d in data]
print(result)

# OUTPUT
# [[], [], ['around_the_world'], ['around_the_globe'], [], [], [], []]

answered Oct 5, 2018 at 5:26

benvc

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1 Comment

Beginner Over a year ago

True! I am learning from many answers. I am really glad with that

Albin Paul · Accepted Answer · 2018-10-05 05:27:56Z

1

I used itertools for this . for more info flatten list of list in python

import itertools
a=[[], [], [['around_the_world']], [['around_the_globe']], [], [], [], []]
a = [list(itertools.chain(*li)) for li in a]
print(a)

Output

[[], [], ['around_the_world'], ['around_the_globe'], [], [], [], []]

answered Oct 5, 2018 at 5:27

Albin Paul

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8 Comments

Beginner Over a year ago

Can I know what is the list() and * for?

U13-Forward Over a year ago

@Beginner list() is converting something to list and * is to unpack something

Albin Paul Over a year ago

It is for converting a generator object to a list , [<itertools.chain object at 0x7f471409b470> , ...... ] this is the output of itertools.chain . list() is used to convert this into the output you see above

Albin Paul Over a year ago

* is essentially for unpacking eg if we want some variable amount of arguments into a function then we can put all the arguments into a list and the call functioncall(*thatlistname) and that will unpack the arguments into the function as arguments

benvc Over a year ago

@Beginner - google "splat" or "splatting" to learn more about the * operator.

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U13-Forward · Accepted Answer · 2018-10-05 05:32:21Z

1

Try next with iter:

a = [[], [], [['around_the_world']], [['around_the_globe']], [], [], [], []]
print([next(iter(i),[]) for i in a])

Output:

[[], [], ['around_the_world'], ['around_the_globe'], [], [], [], []]

answered Oct 5, 2018 at 5:32

U13-Forward

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vash_the_stampede · Accepted Answer · 2018-10-05 17:13:15Z

1

All the short methods look to have been resolved here is a expanded explanation of what is happening in most these processes. Pretty much you are unpacking the nested list and not touching the empty lists.

a = [[], [], [['around_the_world']], [['around_the_globe']], [], [], [], []]
result = []

for i in a:
    if i == []:
        result.append(i)
    else:
        result.append(*i)

print(result)
# [[], [], ['around_the_world'], ['around_the_globe'], [], [], [], []]

answered Oct 5, 2018 at 17:13

vash_the_stampede

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1 Comment

vash_the_stampede Over a year ago

@Beginner no prob :)

blhsing · Accepted Answer · 2018-10-05 05:27:39Z

0

Since you want to flatten the inner sub-lists, you can use list comprehension within a list comprehension:

[[i for s in l for i in s] for l in a]

This returns:

[[], [], ['around_the_world'], ['around_the_globe'], [], [], [], []]

answered Oct 5, 2018 at 5:27

blhsing

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3 Comments

blhsing Over a year ago

Glad to be of help. Do mark what you think is the best answer as accepted once you've reviewed them all. :-)

U13-Forward Over a year ago

@blhsing Yeah should mark, but still have to way a few more minutes

vash_the_stampede Over a year ago

Don't count @U9-Forward out yet he got some tricks up his sleeve!

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