questions related to numpy indexing routines, in particular, slicing, indexing and concatenation
Read more:
Questions tagged [numpy-slicing]
518 questions
1
vote
0 answers
Numba TypingError when indexing 2D array with 2D array
I'm trying to index a 2D array with another 2D array which works fine in Numpy, but I want to use it in a function decorated with Numba's njit decorator, which gives me this error:
TypingError: No implementation of function Function(
kynnemall
- 855
- 9
- 26
1
vote
2 answers
numpy joint two np.arrays in weird manner
I have to np.arrays which I need to join in a really weird manner. Unfortunately the shapes are givn, I can neither change output nor input.
frequencies =
[100. 200.] (2,)
and
values =
[[1. 2.]
[3. 4.]
[5. 6.]
[7. 8.]] (4, 2)
The required…
Michael I.
- 11
- 1
1
vote
0 answers
Slice array based by providing string ':' as index in Numpy
I am in a position to extract whole data from an array. The simplest method would be simply passing array[:]. However, I want to make it automated as part of the larger project where the index would be varying with the data format. Therefore, is it…
sundar_ima
- 3,604
- 8
- 33
- 52
1
vote
1 answer
Adding block-constant matrices in numpy
Let's say we have a
n*n matrix A
m*m matrix B
a vector b=[b_1,...,b_m] of block sizes with b_1 + ... + b_m = n and b_i >= 1.
Then I define a n*n block matrix B_block whose (i,j)-th block is a b_i*b_j matrix of constant value B_{ij}. How can I…
Julian
- 189
- 3
1
vote
2 answers
Numpy Array: Slice several values at every step
I am trying to extract several values at once from an array but I can't seem to find a way to do it in a one-liner in Numpy.
Simply put, considering an array:
a = numpy.arange(10)
> array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
I would like to be able to…
soubaboy
- 13
- 3
1
vote
2 answers
What is the Numpy slicing notation in this code?
# split into inputs and outputs
X, y = data[:, :-1], data[:, -1]
print(X.shape, y.shape)
Can someone explain the second line of code with reference to specific documentation? I know its slicing but the I couldn't find any reference for the…
Purab Bajaj
- 21
- 4
1
vote
1 answer
Indexing ndarray with unknown number of dimensions with range dynamically
I have data array with unknown shape and array bounds of bounds for slicing data. This code is for 3D data, but is there any way of generalizing this to N-dim?
for b in bounds:
l0, u0 = b[0]
l1, u1 = b[1]
l2, u2 = b[2]
a =…
Nikola Jovišić
- 21
- 4
1
vote
1 answer
Numpy subarrays and relative indexing
I have been searching if there is an standard mehtod to create a subarray using relative indexes. Take the following array into consideration:
>>> m = np.arange(25).reshape([5, 5])
array([[ 0, 1, 2, 3, 4],
[ 5, 6, 7, 8, 9],
…
BorjaEst
- 390
- 2
- 11
1
vote
2 answers
multiply a vector and a matrix to create a 3D matrix in numpy
I have a matrix A of zise MxN, and vector b of size L.
how can I create a matrix C of size MxNxL such that:
C[m, n, k] = A[m, n] * b[k]
pretty much the same as dot product of two vectors to create 2D matrix, but with one dimention higher.
I had…
Itamar beeri
- 21
- 3
1
vote
1 answer
Slicing a 3D tensor with a 1D tensor-index in PyTorch
How can I slice a 3D tensor using a 1D tensor? For instance, consider the following 2 tensors: t of size [Batch, Sequence, Dim]; and idx of size [Batch]. The values of idx are restricted to be integers between 0 and Sequence-1.
I need tensor idx to…
Oren
- 171
- 1
- 8
1
vote
1 answer
How can I extract a set of 2D slices from a larger 2D numpy array?
If I have a large 2D numpy array and 2 arrays which correspond to the x and y indices I want to extract, It's easy enough:
h = np.arange(49).reshape(7,7)
# h = [[0, 1, 2, 3, 4, 5, 6],
# [7, 8, 9, 10, 11, 12, 13],
# [14, 15, 16, 17, 18, 19,…
OliverBunting
- 69
- 5
1
vote
3 answers
Printing columns of a list of arrays
I have the following list
import numpy as np
Y = [np.array([[1, 4, 7],
[2, 5, 8]]),
np.array([[10, 14, 18],
[11, 15, 19],
[12, 16, 20],
[13, 17, 21]]),
np.array([[22, 26, 31],
[24, 28, 33],
[26, 30,…
Amelia
- 97
- 8
1
vote
1 answer
Slicing every second row and column of a 3d numpy array, making a new array
I have a NumPy array of dimension 698x64x64 (64rows, 64columns)
I would like to slice it into a new array of 698x32x32 by taking every second row and column of the original array. How do I do that?
Tan Jian Sean
- 35
- 7
1
vote
0 answers
How to reduce memory consumption while splitting a Pandas DataFrame
I have a pandas dataframe which has more than 5 millions rows. I try to slice it (time series to supervised frame) by using the function below. However it consumes too much ram and collaps during long sequences (look_back, forecast_horizon). As I…
ast
- 35
- 1
- 7
