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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1 answer
Crop out background in an image - NumPy / Python
I have the following image extracted. Background value is 170, I need to extract the polygon with a minimum of 170 values.
for the image is like below
I would like to have a processed image as below
I can implement a nested for loop and iterate…
noone
- 6,168
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4 answers
How to change referenced numpy arrays to a slice of itself?
Consider the following operation and slicing applied to two numpy arrays:
In [1]: import numpy as np
In [2]: a = np.array([1,2,3,4]) …
bmello
- 1,864
- 3
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1 answer
How do I replace every nth instance in an ndarray?
I have a numpy array atoms.numbers which looks like:
array([27, 27, 27, 27, 27, 27, 57, 57, 57, 57, 57, 57, 57, 57, 27, 27, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 27, 27, 27,…
Dallon Penney
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1 answer
Slicing of a 3d array with use of a 2d array in Numpy
I got a question regarding slicing of a 3d array with use of a 2d array.
largearray is the 3d array which I want to slice with values from the 2d smallarray
array([[[36.914 , 38.795 , 37.733 , 36.68 , 35.411003,
33.494 ,…
Rens Vermeltfoort
- 21
- 4
1
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2 answers
Slicing N+1d Numpy Array using Nd array
In order to test a wide range of parameters on a single value output, I am creating a multi-dimensional array to store the values. However, in order to update the values accordingly, I need to calculate the positions to be updated. In order to make…
Henri Berger
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2 answers
Finding nearest neighbour =, TypeError: only integer scalar arrays can be converted to a scalar index
I made a function to find the nearest neighbour to a point for a homemade knn classifier.
I did the following:
Defined a function euclid_dist(x,y) to find the distance between two points on a 2-d plane.
Defined a function nearest_neigh(p, points,…
xoxoxoxoxoxo
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2 answers
Numpy: apply function over arbitrarily oriented slices of array
Is there a way to apply a function over general slices of a multidimensional array?
As an example, given a 4D input array representing a color video [frame, y, x, color_channel], we would like to apply a 2D image filter to all 2D slices in [y,…
Hugues
- 2,865
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1 answer
Broadcasting/Vectorizing inner and outer for loops in python/NumPy
Purpose
I have turned a double for loop into a single for loop using vectorization. I would like to now get rid of the last loop.
I want to slice an Nx3 array of coordinates and calculate distances between the sliced portion and the remaining…
Charlie Crown
- 1,071
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1 answer
Numpy slicing a fixed length on two axis based on different starting index given by two arrays
For example, I have nparray:
a = np.arange(48).reshape((3,4,4))
'''
[[[ 0 1 2 3]
[ 4 5 6 7]
[ 8 9 10 11]
[12 13 14 15]]
[[16 17 18 19]
[20 21 22 23]
[24 25 26 27]
[28 29 30 31]]
[[32 33 34 35]
[36 37 38 39]
[40 41 42 43]
…
Jason
- 3,166
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1 answer
How do we split a numpy array at multiples of a number? (eg: array 1 : 0-33, array 2: 34-66, array 3: 67-100)
I have been trying to split a n dimensional array. I want to split it at multiples of 100//3 (=33)
I want to split array of length 100 into 3 groups such that
group 1 is from indices 0-33
group 2 is from 34-66
group 3 is from 67-100
This is what I…
NewbietoPython
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1
vote
1 answer
Extract mask from 3D RGB image using a 1D Boolean array
I have a 3D image which is a numpy array of shape (1314, 489, 3) and looks as follows:
Now I want to calculate the mean RGB color value of the mask (the cob without the black background). Calculating the RGB value for the whole image is…
Olympia
- 457
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1 answer
How to create a Numpy Index with colons everywhere except at one variable coordinate?
I would like to create an index in the form of
[:, :, :, 0, :, :, :, :]
where the position of 0 is determined by a variable, say axis to slice a NumPy array. Obviously there are two special cases that are easy to treat:
axis = 0 would be…
MikeL
- 2,369
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1
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1 answer
How to *actually* delete a column from numpy structured array (so that it won't show up in binary file)
I have a structured array which is loaded from a binary file.
In [85]: dx = np.dtype([('op', '
Mehrdad
- 1,186
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1 answer
How to interpret this kind of NumPy indexing: a[2::2, ::2]?
Can any one tell how to interpret this kind of addressing : a[2::2, ::2]? I have no idea how to use this kind of indexing.
a = np.random.random((6,6))
print(a)
[[0.17948771 0.61436323 0.48768101 0.20540278 0.15331527 0.17766787]
[0.40028608…
Flying pig
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- 27
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1 answer
Taking different columns from each 2D slice of a 3D numpy array
Assume the following 3D numpy array:
array([[[4, 1, 3, 5, 0, 1, 5, 4, 3],
[2, 3, 3, 2, 1, 0, 5, 5, 4],
[5, 3, 0, 2, 2, 2, 5, 3, 2],
[0, 3, 1, 0, 2, 4, 1, 1, 5],
[2, 0, 0, 1, 4, 0, 3, 5, 3]],
[[2, 2, 4, 1, 3,…
Deathcrush
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