CODEWITHSUNDEEP
pythonarrayslist
johnhenry
johnhenry

Reputation: 1333

Python - List of lists of different lengths

I need to create a list which contains two lists. Something like

biglist = [list1,list2]

with 

list1 = [1,2,3]
list2 = [4,5,6,7,8]

where list1 and list2 have DIFFERENT length and are imported from file.

I did it the following way:

biglist = []
list1 = #...taken from file. I checked this and it poduces a list exactly how I want it to be: [1,2,3]
biglist.append(list1)

and likewise for list2

but the problem is that I get 

biglist = [array([1,2,3]),array([4,5,6,7,8])]

as opposed to 

biglist = [[1,2,3],[4,5,6,7,8]]

and I really don't want the array thing, I prefer to have simple lists. how to get around this?

Upvotes: 3

Views: 16246

Answers (5)

developer_hatch
developer_hatch

Reputation: 16224

Just convert your list1 and list2 (those are confusing names indeed because those are numpy arrays, just a comment) with numpy.ndarray.tolist() method and that's it

biglist = [list1.tolist(), list2.tolist()]

Upvotes: 3

o12d10
o12d10

Reputation: 798

There are potential two ways to approach this:

Native Function: list(object)

   biglist = [list(list1), list(list2)]

Numpy Function: numpy.ndarray.tolist()

   bigList = [list1.tolist(), list2.tolist()]

While the question doesn't ask for an optimal method, but here are additional 2 cents to evaluate the two potential approach. Here, we can design test cases to evaluate the performance of each approach.

import timeit

def test1():
    bigList = [list(list1), list(list2)]

def test2():
    bigList = [list1.tolist(), list2.tolist()]

timeit.timeit(stmt=t1, number=1000)
timeit.timeit(stmt=t2, number=1000)

The output of timeit operation:

>>> timeit.timeit(stmt=t1, number=1000)
0.0024030208587646484

>>> timeit.timeit(stmt=t2, number=1000)
0.0007460117340087891``

Upvotes: 0

Saelyth
Saelyth

Reputation: 1734

  • To create a list with all elements: new_list = list1 + list2

  • To create a list with two lists inside: new_list = [list1, list2]

I think you want the second solution. Notice that a list can contain other datatypes inside. A list can contain ["string", 10, ["another", "list"], a_variable, more_stuff] so creating a new list with more lists inside is easy. Just put each of your desired objects as an item.

Update: I don't know if this would work (never used numpy before) but is worth to try:

new_list = [list(str(list1)[6:-1]), list(str(list2)[6:-1])]

Upvotes: 1

R.A.Munna
R.A.Munna

Reputation: 1709

it seems your biglist is a list of numpy array . So, convert numpy array to list by this way getting your desired output.

np.array(list_name).tolist()

new_biglist = []
for ls in biglist:
    new_biglist.append(ls.tolist())

Upvotes: 0

sp________
sp________

Reputation: 2645

please try:

biglist.append(list(list1))
biglist.append(list(list2))

or if they are numpy arrays

biglist.append(list1.tolist())
biglist.append(list2.tolist())

Upvotes: 4

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