questions related to numpy indexing routines, in particular, slicing, indexing and concatenation
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Questions tagged [numpy-slicing]
518 questions
1
vote
1 answer
Slice based on numpy.argmin results
Let us have a numpy array (float) with shape equal to (36, 2, 400, 400). Let us say the 400 by 400 represents an image. Then for each pixel I would like to find the two values (second dimension) which are when taking the norm over the second…
F.Wessels
- 179
- 11
1
vote
1 answer
Replace 2/3 of a multi-dimensional array given a condition
I have the following data
>>> import numpy as np
>>> original_classes=np.load("classes.npy")
>>> original_features=np.load("features.npy")
These NumPy arrays have the following shapes
>>> original_classes.shape
(12000,)
>>>…
mad
- 2,677
- 8
- 35
- 78
1
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0 answers
How to parallelly slic several matrixes from a image in form of 2D numpy array
Given a image in form of 2D numpy array(etc, [H,W]), I want to slic several matrixes(etc, [N，N] N
MaTiezheng
- 23
- 3
1
vote
4 answers
Creating a discretized version of an array
I have a list that describes a profile, such as the next one:
dat=[(0, 5),(1, 1),(3,1)]
I need to create a discretized version of that profile give a step of time 'dt=0.2'. For instance, the firs column of 'dat' would be:
dt = 0.2
time =…
nekovolta
- 496
- 2
- 14
1
vote
2 answers
Index an array with the rows of another array
For example i have an array as
a= [[[98, 92, 92, 81],
[98, 26, 98, 36],
[83, 39, 96, 73],
[75, 36, 37, 68],
[56, 87, 62, 73]],
[[98, 43, 36, 96],
[92, 88, 94, 71],
[ 7, 24, 33, 18],
…
mohd parvez
- 11
- 2
1
vote
0 answers
Indexing a numpy ndarray in a custom class
I am relatively new to Python and I have written a class that contains a numpy.ndarray (containing ordinary Python int objects) for storing some data.
I would like to implement __getitem__ and __setitem__ in a way that behaves intuitively for…
Harry
- 884
- 1
- 8
- 19
1
vote
2 answers
Combing and then maintaining indicies after numpy Logical Slicing
I am trying to conduct logical slicing on two lists and then concatenate them together while maintaining the original indicies.
Here is what I currently have:
x = np.array([0,12,2,246,13,42,245,235,26,33,235,236,23])
y =…
manninosi
- 13
- 4
1
vote
1 answer
How to scatter/send all possible column pairs to the child processes and find coherence between the columns using python mpi4py? Parallel computation
I've a big matrix/2D array for which every possible column-pair I need to find the coherence by parallel computation in python (e.g. mpi4py). Coherence [a function] are computed at various child processes and the child process should send the…
pluto
- 88
- 8
1
vote
1 answer
Add a column to an array with values from a position in another array if rows match
I have two arrays, one looks like this:
[[1 2 1 0 2 0 1]
[1 2 1 0 2 0 1]
[1 2 1 0 2 0 1]
[1 2 1 0 2 0 1]
[0 1 2 1 0 0 2]
[0 1 2 1 0 0 2]
[0 0 1 0 1 0 3]
[0 0 0 1 1 0 4]
[0 0 0 0 1 0 5]
[0 0 0 0 0 1 6]]
The other looks like this:
[[1 2 1 0 2 0]
[1 1…
Gus
- 193
- 9
1
vote
1 answer
Slicing a multiindex pandas dataframe using xs
I have a df
df_test = pd.DataFrame.from_dict({('group', ''): {0: 'A',
1: 'A',
2: 'A',
3: 'A',
4: 'A',
5: 'A',
6: 'A',
7: 'A',
8: 'A',
9: 'B',
10: 'B',
11: 'B',
12: 'B',
13: 'B',
14: 'B',
15: 'B',
16: 'B',
17: 'B',
…
Jonas Palačionis
- 4,591
- 4
- 22
- 55
1
vote
1 answer
precisely slice a 3d array in python
I want to slice a 3D array
[-500:500]
to subarrays in sequence 100 subarrays of length 2 then one of length 50 then 100 of length 2 then one of length 50, and I wish every subarray is spaced by length one from the following.
Elsaid Younes
- 70
- 7
1
vote
1 answer
Comparing 2 CSV files with different length and find out additional data
I have two CSV files, both have different numbers of rows and Columns, in File 1, I have the below structure,
PRODUCT NAME
PRODUCT TYPE
PRODUCT SERIAL
Galaxy S6
Android Phone
IAJ83934830485
Surface Pro
Windows Tablet
IM94545435493
iPhone…
re-learn
- 13
- 3
1
vote
1 answer
Slicing Numpy ndarray
I have used numpy to split a string at each ,. The output shows the split words. When I want to retrive first element, I get the following error:
IndexError: too many indices for array: array is 0-dimensional, but 1 were indexed.
Code
item =…
Lima
- 11
- 2
1
vote
0 answers
Changing values of sliced arrays in numpy
I made a simple array X like this one
import numpy as np
X=np.arange(1,10).reshape(3,3)
Then I made these two arrays that give me the exact same output by slicing X
A=X[:2,:2]
B=X[np.array([0,1])[:,np.newaxis],[0,1]]
If I change a value in A…
Hajin Lee
- 49
- 1
- 3
1
vote
1 answer
Complex indexing of a multidimensional array with indices of lower dimensional arrays in Python
Problem:
I have a numpy array of 4 dimensions:
x = np.arange(1000).reshape(5, 10, 10, 2 )
If we print it:
I want to find the indices of the 6 largest values of the array in the 2nd axis but only for the 0th element in the last axis (red circles…
Puco4
- 491
- 5
- 16