How to declare array of zeros in python or an array of a certain size

Question

I am trying to build a histogram of counts    so I create buckets  I know I could just go through and append a bunch of zeros i e something along these lines   buckets      for i in xrange 0 100       buckets append 0    Is there a  more elegant way to do it  I feel like there should be a way to just declare an array of a certain size   I know numpy has numpy zeros but I want the more general solution

User · Answer

The question says  How to declare array of zeros      but then the sample code references the Python list   buckets          this is a list   However  if someone is actually wanting to initialize an array  I suggest   from array import array  my arr   array  I    0    count    The Python purist might claim this is not pythonic and suggest   my arr   array  I    0 for i in range count      The pythonic version is very slow and when you have a few hundred arrays to be initialized with thousands of values  the difference is quite noticeable

User · Answer

You can multiply a list by an integer n to repeat the list n times   buckets    0    100

User · Answer

Just for completeness  To declare a multidimensional list of zeros in python you have to use a list comprehension like this   buckets     0 for col in range 5   for row in range 10     to avoid reference sharing between the rows   This looks more clumsy than chester1000 s code  but is essential if the values are supposed to be changed later  See the Python FAQ for more details

User · Answer

The simplest solution would be    x00    size   for a buffer of binary zeros  0    size   for a list of integer zeros   In general you should use more pythonic code like list comprehension  in your example   0 for unused in xrange 100    or using string join for buffers

User · Answer

buckets    0    100   Careful - this technique doesn t generalize to multidimensional arrays or lists of lists  Which leads to the List of lists changes reflected across sublists unexpectedly problem

User · Answer

use numpy  import numpy zarray   numpy zeros 100    And then use the Histogram library function

User · Answer

Use this   bucket    None    100 for i in range 100       bucket i     None    100   OR  w  h   100  100 bucket     None    w for i in range h     Both of them will output proper empty multidimensional bucket list 100x100

User · Answer

Depending on what you re actually going to do with the data after it s collected  collections defaultdict int  might be useful

User · Answer

If you need more columns   buckets     0   0   0   0   0   for x in range 0

User · Answer

Well I would like to help you by posting a sample program and its output  Program  -  t input      x  None  t  y   None  t  t  for i in range 1 t 1          x i-1  i        for j in range 1 t 1               y i-1  j-1  j   print x  print y   Output  -  2   1  2     1  2    1  2     I hope this clears some very basic concept of yours regarding their declaration  To initialize them with some other specific values like initializing them with 0  you can declare them as    x  0  10  Hope it helps

[python] How to declare array of zeros in python (or an array of a certain size)

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