questions related to numpy indexing routines, in particular, slicing, indexing and concatenation
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Questions tagged [numpy-slicing]
518 questions
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0 answers
How to access the first two elements for each product_catogory
I have already sorted the dataframe(dfDogNew) based on product_category and quantity_sold. Now I want to access the first two most sold product in each product category, how can I achieve this? I have written a for loop to access them, but the…
0
votes
1 answer
Iterate over inner axes of an array
I want to iterate over some inner dimensions of an array without knowing in advance how many dimensions to iterate over. Furthermore I only know that the last two dimensions should not be iterated over.
For example assume the array has dimension 5…
bayes2021
- 202
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- 7
0
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2 answers
How to apply function to each block of a numpy array in python
I have an n x m array and a function 'switch(A,J)' that takes array (A) and integer(J) input and outputs an array of size n x m. I wish to split my n x m array into arrays of dimension c x c and apply the function with a fixed J to each c x c array…
Tofee
- 1
- 1
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1 answer
How to "spread" a numpy array (opposite of slice with step size)?
Is there a way to spread the values of a numpy array? Like an opposite to slicing with a step size > 1:
>>> a = np.array([[1, 0, 2], [0, 0, 0], [3, 0, 4]])
>>> a
array([[1, 0, 2],
[0, 0, 0],
[3, 0, 4]])
>>> b = a[::2, ::2]
>>>…
trivicious
- 186
- 1
- 8
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0 answers
Filter and modify values from a numpy array based on multiple conditions
I have a number of images and a list of ids associated with each of those images. For the time being I am storing all the images in a list. For e.g.
image_list = [image1, image2, image3, image4, image5, ...]
ids = [1, 2, 1, 1, 1, ...]
I want to…
Ahmad Javed
- 544
- 6
- 26
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2 answers
Unexpected results from Numpy r_
When I use ":n" or "m:" as arguments to np.r_, I get unexpected results that I don't understand.
Here's my code
import numpy as np
B = np.arange(180).reshape(6,30)
C = B[:, np.r_[10:15, 20:26]]
D = C[:, np.r_[0:3,8:11]]
Now all of that worked as…
user2983936
- 25
- 5
0
votes
1 answer
Get each item while slicing (:) a numpy matrix
I have been looking for a solution to this for a while. I am trying to use as few loops in my code as possible, so I've been trying to set slices of the numpy arrays instead.
I have a large array of size (s, s, s, s), but you can think of it as…
Alenna Spiro
- 95
- 5
0
votes
1 answer
How to get index slicing given subset and original array
import numpy as np
origin = np.arange(12).reshape(4, 3)
"""
[0 1 2
3 4 5
6 7 8
9 10 11]
"""
subset = origin[1:3, :2]
"""
[3 4
6 7]
"""
How can I get index slices [1, 2] and [0, 1] given subset and origin assuming subset are contiguous part of…
LeonM
- 23
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- 6
0
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1 answer
Downsampling 3D array with numpy
Given array:
A = array([[[1, 2, 3, 1],
[4, 5, 6, 2],
[7, 8, 9, 3]]])
I obtain the following array in the forward pass with a downsampling factor of k-1:
k = 3
B = A[...,::k]
#output
array([[[1, 1],
[4, 2],
…
Average Leaner
- 23
- 2
0
votes
1 answer
Applying list of slices representing 2D patches to 3D numpy array?
I have a numpy array representing an image (but for now assume the image only has a single channel).
i = np.arange(5*5*1).reshape((5, 5))
array([[ 0, 1, 2, 3, 4],
[ 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14],
[15, 16, 17, 18,…
KDecker
- 6,928
- 8
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- 81
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2 answers
Upsampling using Numpy
I want to upsample a given 1d array by adding 'k-1' zeros between the elements for a given upsampling factor 'k'.
k=2
A = np.array([1,2,3,4,5])
B = np.insert(A,np.arange(1,len(A)), values=np.zeros(k-1))
The Above code works for k=2.
Output: [1 0 2 0…
Rikudo Sennin
- 3
- 2
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votes
0 answers
Is there a keyword for colon (:) indexing in python?
Is there a keyword for ":" in python indices similar to "Ellipsis" for "..."? In multidimensional arrays, I need to sometimes access an entire dimension and sometimes a single slice. I do this by defining my indices in variables. However, I can save…
jestubbe
- 1
- 1
0
votes
1 answer
Recasting NumPy array slice with astype
The code
a = 100. * np.random.randn(200)
a = a.astype(int)
recasts a as an array of integer numbers. Meanwhile, the code
a = 100. * np.random.randn(200) …
JustLearning
- 1,435
- 1
- 1
- 9
0
votes
2 answers
how to use fromiter and ndnumerate together
I'm currently trying to manually implement a function to represent the KNN graph of a set of points as an incidence matrix, and my idea was to take the rows of an affinity matrix(n x n matrix representing the distance between the n points),…
Joshua Ferguson
- 43
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- 5
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votes
1 answer
How can I use a 3d array of indices for a 2d array slicing in Numpy
I have 2 arrays as input. On array as output. Array a holds the data and is of shape (N,M), while array b holds the indices and is of shape (N,X,2). The resulting array should be of shape (N,X), with the values taken from a.
Right now it only works…
Gildur7161
- 21
- 6