CODEWITHSUNDEEP
pythonlistnested-lists
sebko_iic
sebko_iic

Reputation: 341

Append two individual lists to list of lists

Let's say I have:

a=[1,2,3]
b=[4,5,6]

Now I want to create a list of list from a and b, I would do it like this:

c=[a,b]=[[1,2,3],[4,5,6]]

As a.append(b) would result in: [1,2,3,b]=[1,2,3,[4,5,6]]

Now let's say there exists anew list which I want to append to c:

d=[7,8,9]

I now have to do c.append(d) to get [[1,2,3],[4,5,6],[7,8,9]]

Because

e=[c,d]=[[[1,2,3],[4,5,6]],[7,8,9]]

How can I get a list of list from individual lists without know how my lists are structured?

Upvotes: 4

Views: 1499

Answers (3)

Paul Rooney
Paul Rooney

Reputation: 21619

The two actions you are describing are distinctly different. The first is creating the outer list (a.k.a. c) and the second is appending to it.

To make the process more uniform you can just start off with an outer list and append all the child lists to it.

c = []
a=[1,2,3]
b=[4,5,6]
d=[7,8,9]

c.append(a)
c.append(b)
c.append(d)

c is now

[[[1,2,3],[4,5,6]],[7,8,9]]

Upvotes: 1

ZWang
ZWang

Reputation: 892

A bit roundabout of a way but looks nice, using numpy

a = np.array([[1,2,3]])
b = np.array([[4,5,6]])
c = np.append(a,b,axis=0)
print(c.tolist())

gives you

[[1,2,3],[4,5,6]]

Appending another list in the same way keeps the structure of list of lists, for example

d = np.array([[7,8,9]])
e = np.append(c,d,axis=0)
print(e.tolist())

[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

Now this is quite roundabout. I would just keep everything in numpy arrays if possible.

EDIT: Figured out how to do this without numpy

Simply state each list as a list of lists to begin with

a = [[1,2,3]]
b = [[4,5,6]]
a.extend(b)
print(a)

[[1,2,3],[4,5,6]]

Furthermore you can do this

d = [[7,8,9]]
a.extend(d)
print(a)

[[1, 2, 3], [4, 5, 6], [4, 5, 6]]

Upvotes: 1

The Pilot Dude
The Pilot Dude

Reputation: 2227

Try this:

a = [1,2,3]
b = [4,5,6]
c = []

c.append(a)
c.append(b)

This should work, and only takes 2 simple lines.

Upvotes: 2

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