Merging ND array into single array and list

Question

What I have is:

x = array([a, a, a, a, a, a],
          [b, b, b, b, b, b],
          [................],
          [z,z,z,z,z,z,z,z,])

I am looking for a way about:

i. How to covert this array into a 1D array x = array[a,a,a,a,a,a,a,a,b,b,b,b,b,..,z,z,z] and a 1D list x = [a,a,a,a,a,a,a,b,b,b,b,b,...,z,z,z].

ii. Calculating the exact dimensions of this array: I tried len(x[0]) and len(x) to get the both dimensional coordinates, but this way seems a bit hackish. Is there any built-in function to get the dimensions of an array?

Note: some of the array values are positive integers, some of them are floats, some of them are negative floats, and some of them are negative integers.

Many thanks in advance.

wim · Accepted Answer · 2012-09-18 07:38:52Z

2

I use np.ravel for this task.
Just call the list constructor if that's how you want output.
.shape will give you the number of rows and columns, respectively, but you don't actually need to know them.

>>> import numpy as np
>>> a = np.random.random_integers(0, 9, (3, 4))
>>> a.shape
(3, 4)
>>> print a
[[9 5 1 8]
 [3 1 3 1]
 [3 9 6 6]]
>>> a.ravel()
array([9, 5, 1, 8, 3, 1, 3, 1, 3, 9, 6, 6])
>>> list(a.ravel())
[9, 5, 1, 8, 3, 1, 3, 1, 3, 9, 6, 6]

edited Sep 18, 2012 at 7:38

answered Sep 18, 2012 at 7:33

wim

368k114 gold badges682 silver badges819 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

saifuddin778 Over a year ago

This works! fine. All I had to do is to have some modifications with the files and apply the np.ravel(). I am done. Thanks a million. :-)

seberg Over a year ago

There is also .flat, which is just an iterator but enough for such purpose. The advantage is that .ravel() may have to create a copy of the data. It doesn't matter for you I am sure, but it can be a nice feature.

Vorticity · Accepted Answer · 2012-09-18 07:25:24Z

1

To create a 1D array from an ND array, use ndarray.flatten()

x = array([a, a, a, a, a, a],
      [b, b, b, b, b, b],
      [................],
      [z,z,z,z,z,z,z,z,])
x.flatten()

To get a list from this, use ndarray.tolist()

xlist = x.tolist()

To get the dimensions of an array, use ndarray.shape

print x.shape
(4, 6)

answered Sep 18, 2012 at 7:25

Vorticity

4,9864 gold badges36 silver badges54 bronze badges

2 Comments

Mu Mind Over a year ago

for 1D list, you probably want x.flatten().tolist()

saifuddin778 Over a year ago

working with flatten simply allocates every tuple into a single array. I need a single array like x = [a,a,a,a...z,z,z,z] which lists everything from that multi-dimensional array into a serialized format. :-(

Pierre GM · Accepted Answer · 2012-09-18 08:18:36Z

1

To transform the 2D array as a 1D array, you can use np.ravel(a). If you want to do so in place, you can also use a.shape=-1. The a.flatten method will return a copy of the initial array, which is wasteful.
To transform your 1D array into a list, you can use list(a) or a.tolist(). To transform your 2D array into a flat list, the simpler by far is list(a.flat) (.flat returns a 'flat' iterator). Note that using a.tolist on a 2D array will give you a list of list, while using list(a) will give you a list of arrays.
Use a.shape to get the sizes of a along each dimension, as a tuple with as many elements as dimensions. Note that len(a)==a.shape[0]. With your 2D array, len(a[0])=a.shape[1].

answered Sep 18, 2012 at 8:18

Pierre GM

20.5k3 gold badges58 silver badges67 bronze badges

Comments

gabitzish · Accepted Answer · 2012-09-18 07:03:37Z

0

Merge arrays into a new array :

newArray = array()
for y in x
  newArray += y

find length :

len(newArray)

answered Sep 18, 2012 at 7:03

gabitzish

9,7117 gold badges47 silver badges67 bronze badges

2 Comments

Vorticity Over a year ago

To create a 1D array use ndarray.flatten()

saifuddin778 Over a year ago

gabitzish and Vorticity: both of the methods are not working. I want to get a single array like array[a,a,a,a,...z,z,z,z] without any objects or tuples in them. Just a serialized list. It's not happening with the methods you guys specified.

Collectives™ on Stack Overflow

Merging ND array into single array and list

4 Answers 4

2 Comments

2 Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

2 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related