Tagged Questions
2
votes
2answers
43 views
Numpy, python: automatically expand dimensions of arrays when broadcasting
Consider the following exercise in Numpy array broadcasting.
import numpy as np
v = np.array([[1.0, 2.0]]).T # column array
A2 = np.random.randn(2,10) # 2D array
A3 = np.random.randn(2,10,10) # 3D
...
1
vote
2answers
57 views
How to average over a 2-D array?
I have a 2-D numpy array of shape (256,128) and I would like to average every 8 rows of the 256 together so I end up with a numpy array of shape (32,128) Is there any way to average just the one ...
2
votes
1answer
410 views
joining two numpy matrices
If you have two numpy matrices, how can you join them together into one? They should be joined horizontally, so that
[[0] [1] [[0][1]
[1] + [0] = [1][0]
...
2
votes
1answer
59 views
Multiplication of Multidimensional matrices (arrays) in Python
First of all, I am aware that matrix and array are two different data types in NumPy. But I put both in the title to make it a general question. If you are editing this question, please feel free to ...
4
votes
2answers
116 views
Reverse an arbitrary dimension in an ndarray
I'm working with an n-dimensional array, and I'd like a way to reverse a numbered dimension. So rather than
rev = a[:,:,::-1]
I'd like to be able to write
rev = a.reverse(dimension=2)
or ...
1
vote
1answer
38 views
Creating rank 3 numpy arrays
I would like to create a rank 3 array, using numpy, such that the array resembles a stack of 9x9 rank 2 arrays. Each of these arrays will be completely filled with ones, twos, threes, etc.
So, ...
3
votes
1answer
29 views
Cleanest way to merge two same-shape arrays in Numpy
We have some arrays of the same shape and want to merge them.
By "merge", I mean output a new array with the sum of each i,j in each of the arrays in each position.
import numpy as np
first = ...
1
vote
2answers
53 views
Array Indexing in multi dimensional numpy array
I'm new to numpy and trying to understand the following example from here. I'm having trouble understanding the output of
>>> palette[image]
When the indexed array a is multidimensional, ...
1
vote
0answers
52 views
creating and manipulating 3d arrays
I am (very) new to python, previously a Matlab user.
I try to create code to load times series into the rows of a matrix [serie1, 2, 3, etc.] and then manipulate those time series into a loop (see ...
2
votes
2answers
75 views
Iterating two arrays, without nditer, in numpy?
Consider a specification of numpy arrays, typical for specifying matplotlib plotting data:
t = np.arange(0.0,1.5,0.25)
s = np.sin(2*np.pi*t)
Basically, this stores the x coordinates of our (x,y) ...
3
votes
1answer
1k views
numpy reverse multidimensional array
What is the simplest way in numpy to reverse the most inner values of an array like this:
array([[[1, 1, 1, 2],
[2, 2, 2, 3],
[3, 3, 3, 4]],
[[1, 1, 1, 2],
[2, 2, 2, 3],
[3, 3, 3, ...
1
vote
1answer
73 views
Selecting some dimensions from a multi-dimensional array
I have a 4-D array, and I need to process all 1-D vectors from this array along a given dimension. This works well:
def myfun(arr4d,selected_dim): # selected_dim can only be 2 or 3
...
2
votes
6answers
108 views
Python: Find number of occurrences of given array within two-dimensional array
How best to find the number of occurrences of a given array within a set of arrays (two-dimensional array) in python (with numpy)?
This is (simplified) what I need expressed in python code:
patterns ...
0
votes
2answers
49 views
Numpy array subset - unexpected behaviour
I'm trying to copy a subset of a numpy array (to do image background subtraction - but that's by the by). I don't understand what's wrong with the following - I've demonstrated it interactively ...
1
vote
1answer
101 views
numpy divide row by row sum
How can I divide a numpy array row by the sum of all values in this row?
This is one example. But I'm pretty sure there is a fancy and much more efficient way of doing this:
import numpy as np
e = ...
