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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2 answers
How to slice every element of nparray and store it in new nparray?
If this is the nparray i have
arr_str = np.array(['10', '100', '301', '23423'])
I want to convert into like this using slicing
get the last char in the str a[-1] where a is element in nparray
arr_slice = np.array(['0', '0', '1', '3'])
just like…
abhinit21
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1 answer
What is mechanism of using sliced Numpy arrays in a tuple assignment (Python)?
I know that tuple assignment in Python such as the following
a, b = b, a
works by first packing b and a into a tuple (b, a) and then unpacking it to a and b, so as to achieve swapping two names in one statement. But I found that if a and b are…
ihdv
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1
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3 answers
Properties of numpy array
Suppose we have a numpy array.
a = np.array([[1,2,3],[4,5,6], [7,8,9]])
Now, if I want to extract Columns 0 and 2, it would require doing something like
b = a[:, [0, 2]]
However, if we try to find properties of b by executing b.flags, we…
Sudipta Lal Basu
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1 answer
Getting indices of different lengths to slice a multidimensional numpy array
Given these arrays,
R = np.array([[ 5., 3., 2., 7., 3., 6., 8., 9., 10., 55.],
[ 5., 4., 2., 7., 3., 6., 8., 10., 10., 55.]])
F = np.array([[ 0.2 , 0.4 , 0.1 , 0.3 , 0.25, 0.25, 0.2 , 0.1 , 0.1 , 0.1 ],
…
PJORR
- 71
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1
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1 answer
Vectorizing for loop using splicing in NumPy
I have this for loop:
blockSize = 5
ds = np.arange(20)
ds = np.reshape(ds, (1, len(ds))
counts = np.zeros(len(ds[0]/blockSize))
for i in range(len(counts[0])):
counts[0, i] = np.floor(np.sum(ds[0, i*blockSize:i*blockSize+blockSize]))
I am…
joepython
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1
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2 answers
How to mark data as anomalies based on specific condition in each interval
I try to search for this problem many places and couldn't find the right tools.
I have a simple time series data,
print(anom)
0 0
1 0
2 0
3 0
4 0
..
52777 1
52778 1
52779 0
52780 1
For any…
T PHo
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1
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2 answers
batched tensor slice, slice B x N x M with B x 1
I have an B x M x N tensor, X, and I have and B x 1 tensor, Y, which corresponds to the index of tensor X at dimension=1 that I want to keep. What is the shorthand for this slice so that I can avoid a loop?
Essentially I want to do this:
Z =…
Megan Hardy
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1
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1 answer
Bad performance of numpy slicing in function
I have example code like
import numpy as np
nbins = 1301
init = np.ones(nbins*2+1)*(-1)
init[0] = 0
init[1::2] = 0
z0 = np.array(init, dtype=np.complex128, ndmin=1)
initn = z0.view(np.float64)
deltasf = np.linspace(-10, 10, nbins)
gsf =…
wa4557
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1
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1 answer
view of numpy with 2D slicing
Numpy uses a view object to minimize memory copying. The code below slices the original ndarray using index list. The result is None, which means arr[ [0, 3] ] is allocated its own memory.
arr = np.arange(5)
print(arr[ [0, 3] ].base)
In case of…
Jonghun yoo
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- 3
1
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1 answer
Numpy slicing with list
I'm trying to slice an Ndarray a with a list b. But the behaviour is not as I would expect it. What do I have to change to get the wanted result?
a = np.arange(27).reshape(3,3,3)
b = [2,2]
Actual behaviour:
a[:,b]
array([[[ 6, 7, 8],
[…
michmest
- 25
- 4
1
vote
1 answer
Slice Non-Contiguous and Contiguous Columns in Pandas to the Last Column in DataFrame
I am fairly new to python and want to get non-contiguous columns in pandas, but can seem to figure it out. I know in R it could be done like df[:, c(1, 3:)] to select columns 1, 3 to end of columns when using indexing. Just want to know how that is…
GSA
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0 answers
A question about time taken in numpy array assignment with and without slices
I was trying to understand the assignment of values to slices of NumPy arrays. In particular, if sliced assignments are slower than 'less sliced' assignments.
Example:
a[0,:10] = 5
vs
a[0:1,:10] = 5
This inadvertently landed me on a situation where…
figs_and_nuts
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1
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1 answer
Using the colon operator to slice columns in numpy when it might be a vector or might be a matrix
I have two general functions Estability3 and Lstability3 where I would like to evaluate both two dimensional slices of arrays and one dimensional ranges of vectors. I have explored the error outside the functions in a jupyter notebook with some of…
StevenJD
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1
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1 answer
slicing python list beyond its length
I have to slice a Python list/numpy array from an index to -dx and +dx.
where dx is constant. for example:
(the position/index that contains 1 only for illustration, as the center index).
A = [0, 0, 0, 0, 1, 0, 0, 0, 0]
dx=3
print(A[4-dx: 4+dx+1]) …
tetukowski
- 63
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1
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3 answers
In numpy, how do I use a list of indices to slice from the second dimension of a 2D array?
Best explained with an example. The following code gives me the result that I want, but I want to avoid the iteration/list comprehension.
import numpy as np
foo = np.array([range(100, 105), range(200, 205), range(300, 305)])
print("Data:\n",…
Thomas
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