How to convert a n dimensional list to single dimensional list python wothout using any inbuilt functions?

Question

l=[1,[1,[1,[1,[1]]]]]

How to convert the above n dimension list into single dimension list without using any inbuilt functions. Here am looking for the logic.

output should be as [1,1,1,1,1]

Please help me on this

Possible duplicate of [Convert multi-dimensional list to a 1D list in Python](http://stackoverflow.com/questions/2961983/convert-multi-dimensional-list-to-a-1d-list-in-python) — direprobs, Apr 18 '17 at 10:35
Do any of the answers in direprobs link help you? This sounds like homework, so you really should show us what you've tried. Doing this without _any_ inbuilt functions is not easy. Are functions like `isinstance`, `type`, or `len` permitted? How about list methods like `.append` or `.extend`? — PM 2Ring, Apr 18 '17 at 10:44
Why did you accept an answer that uses 3 built-in functions when you specified "without using any inbuilt functions"? — PM 2Ring, Apr 18 '17 at 11:11
BTW, that test data isn't very good: if a solution generates the items in the wrong order you won't see it using that list. — PM 2Ring, Apr 18 '17 at 11:12

Mazdak · Answer 1 · 2017-04-18T10:43:41.120

2

Use a recursion function:

In [20]: def ravel(lst):
             for i in lst:
                 if isinstance(i, list): #use  'type(i) is list' if you don't want built-in functions
                     yield from ravel(i)
                 else:
                     yield i
   ....:                 

In [21]: list(ravel(l))
Out[21]: [1, 1, 1, 1, 1]

edited Apr 18 '17 at 10:43

answered Apr 18 '17 at 10:38

Mazdak

100,514
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`isinstance` is built-in... – juanpa.arrivillaga Apr 18 '17 at 10:39
@juanpa.arrivillaga Yep, just updated ;) – Mazdak Apr 18 '17 at 10:44
`type` is a built-in as well ;) – juanpa.arrivillaga Apr 18 '17 at 10:47
Um, `type` is also a built-in function. And I guess the `list` constructor is too. :) But hopefully the OP doesn't _really_ mean to forbid the use of such basic functions. – PM 2Ring Apr 18 '17 at 10:47
Also note that the question is tagged Python 2.7. FWIW, it _is_ possible to do this without using any functions, as shown in my answer, but it's certainly not a very sensible thing to do. ;) – PM 2Ring Apr 18 '17 at 11:09
@PM2Ring Indeed, you are using the EAFP principle (easier to ask for forgiveness than permission). And in that case you don't need any function at all ;) – Mazdak Apr 18 '17 at 11:44
Exactly. EAFP is good in certain situations, but it's rather inefficient when you expect the exception to be raised frequently. – PM 2Ring Apr 18 '17 at 11:46

score 2 · Answer 2 · answered Apr 18 '17 at 11:07

Here's a Python 2 solution that doesn't use any built-in functions.

Like the other solutions we use recursion. If the current item is a list we recurse into it, yielding whatever solutions are found to the previous recursion level. Otherwise we just yield the item.

def flatten(seq):
    for u in seq:
        try:
            for v in flatten(u):
                yield v 
        except TypeError:
            yield u

l = [1, [2, [3, [4, [5]]]]]
flat = [u for u in flatten(l)]    
print flat

output

[1, 2, 3, 4, 5]

Of course, using Python without any of its built-in functions is silly, unless it's for a programming puzzle. The sensible way to do this is:

def flatten(seq):
    for u in seq:
        if isinstance(u, list):
            for v in flatten(u):
                yield v
        else:
            yield u

l = [1, [2, [3, [4, [5]]]]]
flat = list(flatten(l))

In Python 3, you can use the yield from syntax, as shown in Kasramvd's answer.

def flatten(seq):
    for u in seq:
        if isinstance(u, list):
            yield from flatten(u)
        else:
            yield u

l = [1, [2, [3, [4, [5]]]]]
flat = list(flatten(l))
print(flat)

score 1 · Accepted Answer · answered Apr 18 '17 at 10:38

1

Try this,

l = [1,[1,[1,[1,[1]]]]]
def getAsList(l):
     r =[]
     for i in l:
        if type(i) == list:
            r.extend(getAsList(i))
        else:
           r.append(i)
     return r


print getAsList(l)

answered Apr 18 '17 at 10:38

Kajal

724
6
25

2

Don't use `==` for type validation. Instead use `is`. – Mazdak Apr 18 '17 at 10:44
2

You can replace if type(i) == list with if isinstance(i,list) – decadenza Apr 18 '17 at 10:49

greole · Answer 4 · 2017-04-18T10:47:56.790

0

You could stretch the usage of try and except in order to get this done without isinstance

In [44]: def flatten(l, r):
     ...:     for i in l:
     ...:         try:
     ...:            i.count
     ...:            flatten(i, r)
     ...:         except:
     ...:             r.append(i)
In [46]: l=[1,[1,[1,[1,[1]]]]]
In [47]: r = []
In [48]: flatten(l,r)
In [49]: r
Out[49]: [1, 1, 1, 1, 1]

edited Apr 18 '17 at 10:47

answered Apr 18 '17 at 10:39

greole

4,233
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How to convert a n dimensional list to single dimensional list python wothout using any inbuilt functions?

4 Answers4