How can I check whether a numpy array is empty or not

Question

How can I check whether a numpy array is empty or not   I used the following code  but this fails if the array contains a zero   if not self Definition all      Is this the solution   if self Definition    array

User · Accepted Answer

You can always take a look at the  size attribute  It is defined as an integer  and is zero  0  when there are no elements in the array   import numpy as np a   np array      if a size    0        Do something when  a  is empty

User · Answer

http   www scipy org Tentative NumPy Tutorial head-6a1bc005bd80e1b19f812e1e64e0d25d50f99fe2     NumPy s main object is the homogeneous multidimensional array  In Numpy dimensions are called axes  The number of axes is rank  Numpy s array class is called ndarray  It is also known by the alias array  The more important attributes of an ndarray object are         ndarray ndim   the number of axes  dimensions  of the array  In the Python world  the number of dimensions is referred to as rank         ndarray shape   the dimensions of the array  This is a tuple of integers indicating the size of the array in each dimension  For a matrix with n rows and m columns  shape will be  n m   The length of the shape tuple is therefore the rank  or number of dimensions  ndim       ndarray size   the total number of elements of the array  This is equal to the product of the elements of shape

User · Answer

One caveat  though  Note that  np array None  size returns 1  This is because a size is equivalent to np prod a shape   np array None  shape is     and an empty product is 1    gt  gt  gt  import numpy as np  gt  gt  gt  np array None  size 1  gt  gt  gt  np array None  shape     gt  gt  gt  np prod     1 0   Therefore  I use the following to test if a numpy array has elements    gt  gt  gt  def elements array               return array ndim and array size   gt  gt  gt  elements np array None   0  gt  gt  gt  elements np array      0  gt  gt  gt  elements np zeros  2 3 4    24

User · Answer

Why would we want to check if an array is empty   Arrays don t grow or shrink in the same that lists do   Starting with a  empty  array  and growing with np append is a frequent novice error  Using a list in if alist  hinges on its boolean value  In  102   bool                                                                            Out 102   False In  103   bool  1                                                                         Out 103   True  But trying to do the same with an array produces  in version 1 18   In  104   bool np array                                                                    usr local bin ipython3 1  DeprecationWarning  The truth value     of an empty array is ambiguous  Returning False  but in     future this will result in an error  Use  array size  gt  0  to     check that an array is not empty       usr bin python3 Out 104   False  In  105   bool np array  1                                                                Out 105   True  and bool np array  1 2   produces the infamous ambiguity error  edit The accepted answer suggests size  In  11   x   np array     In  12   x size Out 12   0  But I  and most others  check the shape more than the size  In  13   x shape Out 13    0    Another thing in its favor is that it  maps  on to an empty list  In  14   x tolist   Out 14       But there are other other arrays with 0 size  that aren t  empty  in that last sense  In  15   x   np array       In  16   x size Out 16   0 In  17   x shape Out 17    1  0  In  18   x tolist   Out 18        In  19   bool x tolist    Out 19   True  np array          is also size 0  but shape  2 0  and len 2  While the concept of an empty list is well defined  an empty array is not well defined   One empty list is equal to another   The same can t be said for a size 0 array  The answer really depends on  what do you mean by  empty   what are you really test for

[python] How can I check whether a numpy array is empty or not?

Examples related to python

Examples related to numpy