Numpy universal functions are "vectorized" functions operating on elements (element by element) on a Numpy array.
Questions tagged [numpy-ufunc]
198 questions
3
votes
1 answer
Core dimension error when running numba ufunc on dask array
I'm trying to run custom numba vectorized/ufunc functions in a lazy dask pipeline.
When I run the code below I get a ValueError: Core dimension 'm' consists of multiple chunks. I don't understand why m is considered a core dimension. Any idea how I…
Loïc Dutrieux
- 381
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- 16
3
votes
2 answers
How to access lower triangle of N*M*M numpy array
I have a numpy array of the shape arr.shape = N,M,M.
I want to access the lower triangles for each M,M array. I tried using
arr1 = arr[:,np.tril_indices(M,-1)]
arr1 = arr[:][np.tril_indices(M,-1)]
etc, with the kernel dying in the first case, while…
Aayush Desai
- 41
- 5
3
votes
2 answers
Overriding __iadd__ from the right hand side in Python
Imagine I have a class A that is outside of my control (numpy.ndarray is the specific application), and class B within my control (scipy.sparse.coo_matrix). I want to implement in-place addition of B to A without touching class A.
Is this at all…
Anton Akhmerov
- 154
- 9
3
votes
2 answers
How to make element of 3D array into upper triangular and then tranpose it
For example, I got the 3D array below
[[[1,2,3],
[4,5,6]
[7,8,9]],
[[1,3,5],
[2,4,6],
[5,7,9]]
[[1,4,6],
[2,4,7],
[5,8,9]]
]
The first question is that how I can make each element along the first axis become the triangular matrix,…
Nicolas H
- 535
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- 13
3
votes
1 answer
Numpy vectorize for a lambda with multiple arguments
I tried for a while last night to use the various different numpy vectorisation functions for a task (which to be clear is perfectly doable without them), to create linear interpolations between points.
Let's say I have a vector of floats (let's…
Louis Maddox
- 5,226
- 5
- 36
- 66
3
votes
1 answer
why np.std() and pivot_table(aggfunc=np.std) return the different result
I have some code and do not understand why the difference occurs:
np.std() which default ddof=0,when it's used alone.
but why when it's used as an argument in pivot_table(aggfunc=np.std),it changes into ddof=1 automatically.
import numpys as…
SirenL
- 33
- 5
3
votes
1 answer
Fastest Python log-sum-exp in a 'reduceat'
As part of a statistical programming package, I need to add log-transformed values together with the LogSumExp Function. This is significantly less efficient than adding unlogged values together.
Furthermore, I need to add values together using the…
Wilder Wohns
- 33
- 7
3
votes
1 answer
Combined vectorized functions in Numba
I'm using Numba (version 0.37.0) to optimize code for GPU.
I would like to use combined vectorized functions (using @vectorize decorator of Numba).
Imports & Data:
import numpy as np
from math import sqrt
from numba import vectorize,…
jetxeberria
- 187
- 1
- 8
3
votes
1 answer
Map Pandas dataframe based on index, column name and original value?
I would like to map the values of a dataframe to values from a different dataframe (might also be a dict).
The element to which I want to map depends on three things:
the original value,
the index name and
the column name.
For example I have the…
niclash
- 33
- 1
- 5
3
votes
1 answer
Can numpy.add.at be used with 2D indices?
I have 2 arrays:
- image is a NxN array,
- indices is a Mx2 array, where the last dimension stores valid indices into image.
I want to add 1 in image for each occurrence of that index in indices.
It seems like numpy.add.at(image, indices, 1) should…
user1411900
- 384
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- 14
3
votes
1 answer
Numpy power ufunc operating on specific axis
I find it weird that numpy.power has no axis argument... is it because there is a better/safer way to achieve the same goal (elevating each 2D array in a 3D array to the power of a 1D array).
Suppose you have a (3,10,10) array (A) and you want to…
Antonin
- 33
- 3
3
votes
1 answer
How to specify the last index explicitly to np.ufunc.reduceat
Say I have an array
data = np.arange(6)
I want to find the sum of the entire array and the second half using np.add.reduceat.1
If I do it like this:
np.add.reduceat(data, [0, 6, 3])[::2]
I immediately get an error
IndexError: index 6 out-of-bounds…
Mad Physicist
- 107,652
- 25
- 181
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3
votes
1 answer
Numpy: Finding minimum and maximum values from associations through binning
Prerequisite
This is a question derived from this post. So, some of the introduction of the problem will be similar to that post.
Problem
Let's say result is a 2D array and values is a 1D array. values holds some values associated with each element…
mrtpk
- 1,398
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- 38
3
votes
1 answer
Fast and efficient slice of array avoiding delete operation
I am trying to get a slice (for example elements 1-3 and 5-N) of an array A(N,3) avoiding using numpy.delete. And example of the process will be the following:
[[1,2,3],[4,5,6],[7,8,9],[3,2,1]] ==> [[1,2,3],[3,2,1]]
I was hoping to use something…
Basetxerri
- 49
- 3
3
votes
0 answers
numpy ufunc c-api ndarray(dtype=custom_dtype) operaration scalar of custom_dtype
I'm struggling with the situation when I need a code like this to work:
from custom_lib import custom_type, custom_dtype
import numpy as np
a = custom_type(1)
arr = np.array([a,a],dtype=custom_dtype)
arr+a // doesn't work ( No cast function…
vladislav odobesku
- 51
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- 4