CODEWITHSUNDEEP
pythonnumpy
Tengis
Tengis

Reputation: 2819

How to check if an array is 2D

I read from a file with loadtxt like this

data = loadtxt(filename) # id x1 y1 x2 y2

data could look like

array([[   4.      ,  104.442848, -130.422137,  104.442848,  130.422137],
   [   5.      ,    1.      ,    2.      ,    3.      ,    4.      ]])

I can then reduce data to the lines belonging to some id number: 

d = data [ data[:,0] == id]

The problem here is when the data contain only one line.

So my question is how to check the 2-dimensionality of my array data?

I tried checking

data.shape[0]  # num of lines

but for one-liners I get something like (n, ), so this will not work.

Any ideas how to do this correctly?

Upvotes: 13

Views: 31010

Answers (3)

Shalini Baranwal
Shalini Baranwal

Reputation: 3008

one more way:

Look for array.shape:

if it comes like (2,) means digit at first place but nothing after after comma,its 1D. Else if it comes like (2,10) means two digits with comma,its 2D. Similarly how many digits available with comma, that many dimensional array it is.

Simple "array.shape" will help you know that.

Upvotes: 0

imz22
imz22

Reputation: 2938

You can always check the dimension of your array with len(array) function.

Example1:

data = [[1,2],[3,4]]
if len(data) == 1:
   print('1-D array')
if len(data) == 2:
   print('2-D array')
if len(data) == 3:
   print('3-D array')

Output:

2-D array

And if your array is a Numpy array you can check dimension with len(array.shape).

Example2:

import Numpy as np
data = np.asarray([[1,2],[3,4]])
if len(data.shape) == 1:
   print('1-D array')
if len(data.shape) == 2:
   print('2-D array')
if len(data.shape) == 3:
   print('3-D array')

Output:

2-D array

Upvotes: 1

unutbu
unutbu

Reputation: 880777

data.ndim gives the dimension (what numpy calls the number of axes) of the array.

As you already have observed, when a data file only has one line, np.loadtxt returns a 1D-array. When the data file has more than one line, np.loadtxt returns a 2D-array.

The easiest way to ensure data is 2D is to pass ndmin=2 to loadtxt:

data = np.loadtxt(filename, ndmin=2)

The ndmin parameter was added in NumPy version 1.6.0. For older versions, you could use np.atleast_2d:

data = np.atleast_2d(np.loadtxt(filename))

Upvotes: 18

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