questions related to numpy indexing routines, in particular, slicing, indexing and concatenation
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Questions tagged [numpy-slicing]
518 questions
2
votes
2 answers
how to slice a 2d array based on indices given in another 2d array
I have an MxN array called A which stores the data I want. I have another M x N2 array B which stores array indices, and N2
Physicist
- 2,848
- 8
- 33
- 62
2
votes
3 answers
Slice an array into segments
Suppose I have an array [1,2,3,4,5,6,7,8]， and the array is composed of two samples [1,2,3,4], and [5,6,7,8]. For each sample, I want to do a slicing window with window size n. And if there are not enough elements, pad the result with the last…
tczj
- 438
- 4
- 17
2
votes
4 answers
numpy: slice away 2 columns
Consider the following data:
61 1 1 15.04 14.96 13.17 9.29 13.96 9.87 13.67 10.25 10.83 12.58 18.50 15.04
61 1 2 14.71 16.88 10.83 6.50 12.62 7.67 11.50 10.04 9.79 9.67 17.54 13.83
61 1 3 18.50 16.88 12.33 10.13 11.17 6.17 11.25 8.04 …
2020
- 2,821
- 2
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2
votes
2 answers
Trying to understand syntax with index slicing in python matrix
I have been looking over and interpreting some sample code and am having some trouble understanding what is going on with a bit of slicing syntax. For some context I am working on a computational program that uses method of finite differences…
Chase Gammon
- 21
- 3
2
votes
1 answer
How is one supposed to use the arange function when indexing an ndarray?
Let's say I want to select a value from a different column for each row. Then, I might do something like this:
a = np.arange(12).reshape(3, 4)
columns = np.array([1, 2, 0])
a[np.arange(a.shape[0]), columns]
It seems a bit 'ugly' to me to need to…
vandenheuvel
- 349
- 2
- 13
2
votes
1 answer
Assigning values to a numpy array using indices and sub indices
This has bitten me a few times, and I can't tell if it's a bug or a feature.
nums = np.arange(10)
indx1 = np.array([2,4,6,8])
indx2 = np.array([0,3])
It looks like I can index nums either way
nums[indx1][indx2], nums[indx1[indx2]]
outputs…
I.P. Freeley
- 885
- 1
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- 19
2
votes
1 answer
Slicing the channels of image and storing the channels into numpy array(same size as image). Plotting the numpy array not giving the original image
I separated the 3 channels of an colour image. I created a new NumPy array of the same size as the image, and stored the 3 channels of the image into 3 slices of the 3D NumPy array. After plotting the NumPy array, the plotted image is not same as…
Shivam Das
- 23
- 3
2
votes
3 answers
Numpy array : NOT select specific rows or columns
I have a simple numpy array. I want to select all rows but 1st and 6th
I tried:
temp = np.array([1,2,3,4,5,6,7,8,9])
t = temp[~[0,5]]
I get the following error:
TypeError: bad operand type for unary ~: 'list'
What is the correct way to do this?
Anuj Gupta
- 6,328
- 7
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- 55
2
votes
1 answer
split 3D numpy to 3 diffrent arrays
I have numpy.array pf shape (64 , 64 , 64)
I would like to split it on to 3 variables ,so
x.shape ==> (64)
y.shape ==> (64)
z.shape ==> (64)
as each dim represent voxels coordinate (x,y,z) , I tried use dsplit() but no luck. any suggestion?
user3029270
- 59
- 2
- 10
2
votes
1 answer
Selecting a row interval according to a Column value in Pandas
Hi everyone I have a dataset that looks like this
transferid value type
5545 100 X
5123 40 A
5566 35 A
5675 700 X
5235 1100 A
5616 350 A
5772 …
Jesus Rincon
- 136
- 9
1
vote
1 answer
How to extract chunks of a 2D numpy array that has been flattened
I would like to know the best way of extacting chunks of elements from a 2D numpy array that has been flattened. See example python code below which hopefully explains what I want to do a little better.
import numpy as np
nx = 5
nz = 7
numGPs =…
n1ck94
- 41
- 5
1
vote
2 answers
Selecting numpy array on the last axis
I have a 3D array and a 2D array of indices. How can I select on the last axis?
import numpy as np
# example array
shape = (4,3,2)
x = np.random.uniform(0,1, shape)
# indices
idx = np.random.randint(0,shape[-1], shape[:-1])
Here is a loop that…
guyguyguy12345
- 539
- 3
- 11
1
vote
1 answer
I cannot run python runtests.py -v for testing numpy it giving me version issue
I want to run test for numpy library in my local machine but when I simple testing command
like this command
python runtests.py -v
I am keep getting following error
`
Building, see build.log...
Traceback (most recent call last):
File…
Ishaque3 Nizamani
- 51
- 3
1
vote
1 answer
Summing elements in sliding window after applying function to last n elements
I currently have a dataframe formatted as such:
a b c e f
2 3 4 5 1
9 8 6 4 6
1 2 2 2 3
9 8 8 9 1
3 6 8 6 2
. . . . .
. . . . .
7 5 4 1 8
My goal is to apply an adaptive weight function over the last n(4) games in a sliding window. On…
Sentient AI Turing
- 49
- 4
1
vote
1 answer
Slicing numpy arrays in a for loop
I have a multidimentional numpy array of elasticities with one of the dimensions being "age-groups" (0-92 years) and the other "income-groups" (low/high income).
I would like to create a table with the mean elasticities for each combination of…
Stata_user
- 562
- 3
- 14