# Numpy-ndarray Questions

## Fastest way to get dot product of a matrix and each point in the given array

I have an array nx3 of n points, each one has x, y and z coordinate. i need to rotate each point, so i have the rotation matrix 3x3. to do this, i

## Element-wise division with accumulated numbers in Python?

The title may come across as confusing (honestly, not quite sure how to summarize it in a sentence), so here is a much better explanation:

## How to call `__rsub__` properly with a numpy array?

Consider the following snippet: import numpy as np class myclass: def __rsub__(self,

## Reversing the view of a numpy array twice in a jitted function makes the function run faster

So i was testing the speeds of two versions of the same function; one with reversing the view of a numpy array twice and one without. the code is

## structure of np.zeros with multi dimensional shape

I have seen in a program on github which contains img_out = np.zeros(((4,)+(512,1024,3)+(3,))) i am trying to

## Optimizing performance of list comprehension using all indexes in own functions

I have a multi-dimensional matrix (6d) that i need to iterate over in order to make a new 6d-matrix. right now i use list comprehensions to make

## From numpy array, get indices of values list

Like this: >> arr = np.array([[0, 50], [100, 150], [200, 250]]) >>> values = [100, 200, 300] >>> arr in

## Unable to load data from numpy array for SVM Classification

I have images in the numpy format, i have downloaded the data from the

## Get the first three largest values of a 2dnumpy array in python

Hi i have a numpy array for eg. arr = np.random.rand(4,5) array([[0.70733982, 0.1770464 , 0.55588376, 0.8810145 , 0.43711158],

## Occurrence of list in ndarray

I have an rgb image -ndarray- and i want to count the occurrence of some colors like [255,0,0] or [0,0,255] in this image. example of

## Make all the elemant zero except max n element in each row in numpy 2d-array

Let's say i have a 2d numpy array like: [[1, 8, 3, 4, 5], [10,13,13,12,15]] i want to convert all

## Replacing elements in an array from index array

I have two 2d arrays like: a=array[[4,5,6], [0,7,8], [0,9,0]] b = array[[11,12,13], [14,15,16],

## Array won't assign more than 8 characters in python

Array is acting weirdly, i have this code: a=np.array(['dfdfdfdf', 'gulf', 'egypt', 'hijazi a', 'gulf', 'egypt'])

## How to check inner part of 3D array numpy

I have a 3d array a = np.array([[[1,1],[1,1]],[[1,0],[1,0]]]) and i need to check which members are equal to [1,1] and

## How does one acces numpy multidimensionnal array in c extensions?

I have been struggling for a few day to understand the access to numpy arrays in c extension, but i've trouble understanding the

## cannot reshape array of size (x,) into shape (x,y,z,1)

I'm trying to convert a numpy ndarray with a shape of (2200,) to numpy ndarray with a shape of (2200,250,250,1). every

## python: how to shuffle matrix rows according to a list of numbers

I have this numpy array a = [1, 2, 3, 4, 5; 6, 7, 8, 9, 10; 11, 12, 13, 14, 15 ] and a list of numbers [0, 2, 1]. i want to shuffle

## How to extract an array of same dimension as the original array meeting a condition?

The question sounds very basic. but when i try to use where or boolean conditions on numpy arrays, it always returns a

## What is the difference between numpyArr[:,:,:,c] and numpyArr[...,c]?

I've beeen taking deep learning course on coursera. while i was doing my assignment i saw one piece of code on the github. 1.

## Numpy array: Function affects original input object as well

I am working at my personal image augmentation function in tensorflow 2.0. more specifically, i wrote a function

## Downsampling by adding n^dim elements together in numpy/sparse

For a personal project i am trying to downsample a 3d grid, represented as sparse.coo array, with image like data (index encodes

## Euclidean distance: results are different between python and numpy with large number of instances

I am trying two methods to implement the square result of euclidean distance. by numpy: def inference(feature_list):

## numpy array IndexError: 'index out of bound' when a mask is inverted or negated

I have 2 arrays one is mask and the other is the labels: both arrays have the same shape: (pdb) l.shape (178, 201, 101)

## Can't Reshape Numpy Array, even with multiple methods

I am getting a very strange error: print(np.asarray(x[i%len(y)]).shape) x_train = x[i%len(y)] x_train.shape = (1,

## How to add or remove a specific element from a numpy 2d array?

Given the following numpy array: arr = np.array([ [1,2,3], [4,5,6], [7,8,9] ]) delete and return:

## Python NumPy - angled slice of 3D array

Working in numpy, i understand how to slice 2d arrays from a 3d array using

## How to have specific conditions per element for a matrix or 2d array in python?

I have multiple matrices and i want to create another one 'g' based on the previous matrices that i have created. i have a general formula to

## Pytorch: Why is the memory occupied by the `tensor` variable so small?

In pytorch 1.0.0, i found that a tensor variable occupies very small memory. i wonder how it stores so much data. here's the

## Stretch an array and fill nan

I have a 1-d numpy array with length n, and i want to stretch it to m (n<m) and systematically add numpy.nan. for example:

## An elegant/faster way to find the end points of a line on a image?

I've been working to improve the speed of my code by replacing for loops of array operations to appropriate numpy functions. the function

## 3-D Matrix Multiplication in Numpy

I have to multiply two 2-d matrices, bob and tim, in numpy python 3.x bob.shape gives

## Getting the index of the minimum value in each slice of `ndarray`

I am trying to do something that should be straightforward and can be accomplished in a for-loop but i am trying to avoid that. i

## Order the min over ndarrays by keeping information about the original indexes

Consider having a numpy.ndarray d1 with shape (10,n,m). i would like to build a new ndarray o1 with shape

## What is the need of ellipsis[...] while modifying array values in numpy?

Import numpy as np a = np.arange(0,60,5) a = a.reshape(3,4) for x in

## Plotting 2darray with matplotlib

A = np.arange(1,10).reshape((3,3)) plt.plot(a[0],a[1:]) why am i getting: valueerror: x and y must have same first

## Numpy ndarray: understanding slice objects and ":"

Suppose you have: data = np.array([ [ 0, 1 ], [ 0, 1 ] ], dtype='int64')

## Reducing Dimensions using PCA: AttributeError: 'numpy.ndarray' object has no attribute 'items'

I'm trying to implement an example project on dzone

## Declaring new math function using numpy

A simple issue: why does import numpy as np f = np.sin(x) print(f(0.3)) return an error; whereas

## ndarray rows are not displayed each one per line

I have this code: import numpy as np m =

## Mean, variance and standard deviation in python

N,m = map(int,input().split()) a = [] for _ in range(n): a.append(map(int,input().split())) a = numpy.array(a) print

## Create boolean mask for an array of tuples

I have a 2d numpy array with a shape (3, 3) and dtype=object whose elements are tuples of the form (str, str, float). template =

## How to connect Python arrays

I don't understand when it is sum operation or just connect two arrays x = np.arange(10) x #array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

## How to pick up an element randomly in a numpy array?

Enter image description herei am writing script to realize a

## How can I add a string in nparray

Here's my code: age=request.user.allusers.age sex=request.user.allusers.sex index_array = np.array(states) index_array = [val-1

## How to convert a 3 dimensional list into a Dataframe?

I need to convert the following array into dataframe. import numpy as np import pandas as pd arr = [[0, [0.13, 0.24, 0.19]],

## numpy.fromfile seems to be unable to read large files

I wanted to write some very simple python helper tool for my project which is reading binary data from an ecg record. i have found somewhere that

## Python: Insert columns into a numpy array based on mask

Suppose i have the following data: mask = [[0, 1, 1, 0, 1]] # 2d mask ip_array = [[4, 5, 2] [3, 2, 1] [1,

## 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")

## Numpy array with numpy arrays as objects

I'd like to create a numpy ndarray with entries of type ndarray itself. i was able to wrap ndarrays into another type to get it work but i want to

## Writing numpy array in a text file

I have encountered an error while trying to write a numpy error into a text file. to put the question the below code import numpy

## Python :print the cumulative sum of x along axies 0 and 1

Create a array of x shape (5,6) having 30 random integer between -30 and 30 print the cumulative sum of x along axies 0 print the

## Python dictionary creation with conditioned values added

I want to make a dictionary from 2 numpy arrays, arr1 as keys of dictionary and arr2 as values of dictionary. the

## How to convert INDArray to Json in java?

Indarray image = loader.asmatrix(file); how to convert indarray to json string and from json string to indarray. i

## Further optimization with numpy using einsum for stacked matrix-vector multiplication

I have a relatively straightforward case of "particle propagation" using linear matrix transformation. my distribution of particles is