questions related to numpy indexing routines, in particular, slicing, indexing and concatenation
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Questions tagged [numpy-slicing]
518 questions
1
vote
0 answers
NumPy: how to check leading dimension of non-owned array?
In NumPy, one can have arrays which are just pointing towards data that was allocated in a different array in order to avoid deep copies. For example:
import numpy as np
a = np.ones((3,4))
b = a[:2]
Now b just contains a pointer to the array in a,…
anymous.asker
- 1,179
- 9
- 14
1
vote
1 answer
Python Pandas select rows in numpy array on first columns
I have a dataframe like this:
df = pd.DataFrame({'A':[1,2,3], 'B':[4,5,6],'C':[7,8,9],'D':[10,11,12]})
and a list, here arr, that may vary in length like this:
arr = np.array([[1,4],[2,6]])
arr = np.array([[2,5,8], [1,5,8]])
And I would like get…
Nicolas Rey
- 431
- 2
- 6
- 19
1
vote
1 answer
How to efficiently shuffle some values of a numpy array while keeping their relative order?
I have a numpy array and a mask specifying which entries from that array to shuffle while keeping their relative order. Let's have an example:
In [2]: arr = np.array([5, 3, 9, 0, 4, 1])
In [4]: mask = np.array([True, False, False, False, True,…
hikaru_alpha
- 33
- 5
1
vote
1 answer
How to change the order numpy stores the data?
I have a numpy array that I need to change the order of the axis.
To do that I am using moveaxis() method, which only returns a view of the input array, by changing only the strides of the array.
However, this does not change the order that the data…
BayesianMonk
- 540
- 7
- 23
1
vote
1 answer
Why slicing in boolean filtered array is not happening..?
When I try to slice the boolean filtered numpy array it's not changing its value.
please look a
array = np.array([1,2,3,4,5,6,7,8])
array[array>=2]
array([2, 3, 4, 5, 6, 7, 8])
array = np.array([1,2,3,4,5,6,7,8])
array[array>=2][1:5]
array([3, 4,…
AJITH PINNINTI
- 83
- 1
- 4
1
vote
2 answers
How do I enumerate a 2-dimensional NumPy array excluding the first and last rows and columns?
I would like to enumerate the elements of a 2-dimensional NumPy array excluding the first and last row and column (i.e. the ones in the matrix below).
import numpy as np
q = np.zeros((4, 4))
q[1, 1] = 1
q[1, 2] = 1
q[2, 1] = 1
q[2, 2] = 1
# [[0.…
Frank
- 3,029
- 5
- 34
- 43
1
vote
3 answers
slicing periodically for a numpy array
I have a numpy array a = np.arange(100) including 100 numbers.
I wondered to know is there a way to slice it periodically rather than using the conditional statements.
for example, if I want to slice the 1st four numbers + 5th four numbers + 9th…
user14655550
1
vote
1 answer
I'm multiplying a numpy matrix column by a float and getting a strange rounding. What is causing this?
I trying to update the column of a matrix by multiplying it with a float. See the code below.
H = np.array([[1, 2, 3], [4, 5, 6]])
print(H[:, 0] * 0.1)
H[:, 0] = H[:, 0] * 0.1
print(H[:, 0])
Which gives the output:
[0.1 0.4]
[0 0]
Numpy seems to…
ViktorEM
- 13
- 2
1
vote
1 answer
"IndexError: too many indices for array" when trying to count unique items in numpy array column
I have a numpy array called data which has 8 columns and gets recursively manipulated in the rows so it has a variable number of rows each time it passes through the function I need to apply.
Inside that function I have the following line of code…
user14501128
- 21
- 3
1
vote
2 answers
Confused on Index Slicing in python
I am slicing my hour column and when I use slice(1, 3) and slice(0, 3) I get the same results. What am i missing? See in the image below.
Meet Shah
- 73
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1
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0 answers
Combination of slicing and array index in numpy
Looking at the answers to this question: How to understand numpy's combined slicing and indexing example
I'm still unable to understand the result of indexing with a combination of a slice and two 1d arrays, like this:
>>> m =…
shenun
- 85
- 5
1
vote
1 answer
Numpy get values at indices given in array form
I want to get the values at indices of my_array.
indices = np.array([[[0],
[1],
[0]]])
my_array = np.array([[[1.1587323 , 1.75406635],
[1.05464125, 1.29215026],
[0.9784655 , 1.16957462]]])
I should get the…
Anas BELFADIL
- 106
- 9
1
vote
3 answers
finding all the points that belong to a plane using python
I have an mx3 array that is used to create a 3d model. Is there is a fast way to extract all the points that belong to a given plane using numpy or other python functions? The plane will take the Ax+By+Cz+D=0 form. I'm currently looping through all…
yihao ren
- 369
- 1
- 4
- 15
1
vote
4 answers
How to concatenate sliced array to a list in Python
I am trying to merge a sliced array to a list in Python but i get an
error: ValueError: operands could not be broadcast together with shapes `(4,)` `(2,)` .
This is my code:
y = np.array([5,3,2,4,6,1])
row = y[2:6] + np.array([0,0])
I am…
Adrian Zvizdenco
- 13
- 3
1
vote
0 answers
NumPy ndarray slicing and indexing using comma
What basically the commas do in slicing nd array in NumPy?
E.g. for a 3d array, what do these mean?
a[1,2::] a[:2,3:] a[1:2,:]
I means commas in general, how do these thing work while slicing? I know about
a[start:stop:step] but having hard time…
cyclonejet
- 41
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