Questions tagged [numpy]
NumPy is the fundamental package for scientific computing with the programming language Python.
721
questions
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Python function that shears image by n degrees while keeping the relationship between height and width
I am trying to find a method to shear/skew an image horizontally or vertically by n degrees (n ranges from -90 to 90 excluding the terminals) so that the result would meet the following conditions:
...
- 1,522
2
votes
2
answers
41
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Sampling from k circles with different radii
Description: I would like to sample n_points points from k circles whose radii and centers are given as lists.
Note: This is my ...
- 121
0
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0
answers
62
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Python 3 OpenCV script that scans a giant picture to make a video
This is a Python script that I wrote completely by myself. Basically it scans a giant picture to make a video.
They say one picture is worth more than a thousand words. Since a video contains ...
- 1,522
0
votes
1
answer
40
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Extract all elements of array with the given list of coordinates [duplicate]
I have to extract all elements of array with the given list of coordinates and insert into 2*298808 as position given in while loop
How can I compress the code even more?
...
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-1
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1
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50
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0
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0
answers
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Creating an image from data, and slicing it into zxy tile service
I have some data that comes out of a grib file. The values in the grib file come out in shape of (721, 1440). Each value ...
- 408
0
votes
1
answer
59
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Stacking Z axis on multiple [1440x720] DataFrames (X, Y)
Each datum represents a point in a 1440x720 image of the globe, The values are 0-9. Each new layer is of a higher elevation. I need to structure a DataFrame in a ...
- 408
5
votes
0
answers
81
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Python 3 script to make photo collages
I have written a Python script that takes a list of filenames of pictures and generates a photo collage of them. This is my most complex project yet, and I have written it completely by myself (like I ...
- 1,522
2
votes
1
answer
80
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Replace nested for loops when assigning intial conditions in a 4-dimensional array
I create a 4-dimensional (x, y, z, t) array of zero values. I then set the initial values at t = Tmax. To do this, I use a nested for loop. I attempted to improve ...
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2
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1
answer
62
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type hinting/documenting/extension of a Cython lib
I've updated some of the type hinting/documentation in a lib called pygrib. The source documentation
can be found here.
The goal is to extend the ...
- 408
1
vote
1
answer
67
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Solving a 3D heat diffusion PDE
I am trying to solve a heat diffusion type PDE using a finite difference method.
I would like to preface that I have seriously simplified the code. Just so that anyone who tries to help me, doesn't ...
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2
votes
1
answer
68
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dataframe mean outliers to NaN to derive a higher quality mean for area,speed,azimuth
I have some data that represents the area, speed(meters per second), and azimuth(rads) of a polygon. The objective is to determine the mean for each set of parameters. With that mean value, apply a ...
- 408
1
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1
answer
39
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numpy mean azimuth with functools.reduce
From the left to the right column calculating the mean azimuth, and using that mean value to calculate the subsequent columns mean value
data (azimuth radians)
...
- 408
3
votes
1
answer
49
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Making a list of shades and styles for plots
For a section of a much larger program that generates plots, I am creating a list of styles that I can pull from to create a consistent format from plot-to-plot. It works as follows
I have a list of ...
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3
votes
1
answer
97
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pandas dataframe of temps and numpy.linalg.lstsq
The problem is this. Forecast model data indicates at 0700Z the 1000 milibar temps will be -4C°. The forecaster knows that is incorrect, so they choose to make a correction. This correction should ...
- 408
3
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1
answer
118
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Vincenty's distance Direct formulae numpy
I've refactored a function from the pygc library used to generate the great_circle. The Vincenty's equation below can be found ...
- 408
3
votes
1
answer
129
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Numerical integration in Python involving four dimensions
I'm trying to obtain the following S2 from a given S1,
$$
S2(i, j) =
\sum _{k=0} ^i
\sum _{l=0} ^j
S1(k, i-k, j, l)
e^{
-\sqrt{...
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4
votes
1
answer
66
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3D to 4D surface fitter converter
I recently wrote this bit of code while trying to convert a 3D surface fitter to a 4D one. The solution works and I didn't want to leave the next guy to grind out the solution so I made the code as ...
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4
votes
1
answer
106
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pandas conditions across rows and columns
Is there a better way to accomplish this? The function determines the Category for each row based on some conditions. Another set of conditions determines the <...
- 408
1
vote
0
answers
39
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Pandas Numpy Nvector to generate a storm track algorithm
I made previous post here, relating to this topic.
The class uses now uses some additional 3rd party libs nvector & pygc.
...
- 408
1
vote
1
answer
57
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Multiple GeoJSON Feature Collections to a Pandas MultiIndex DataFrame
Edit: The end objective is to monitor the movement of severe weather, determine its vector and make a prediction.
I'm working with a GeoJSON ...
- 408
5
votes
1
answer
443
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Laser physics simulation
This is for a computation for laser physics. The speed is quite slow, which seems to be delayed a lot by the three nested for loops with indices j,k, and l (with comments below). And the computation ...
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1
vote
1
answer
109
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Minimum re-labeling to make an array as close as possible to another one
I have an array with integer labels in [0, n-1], say arr1=[1, 0, 3, 2] with n = 3. And then I have another array again with integer labels in [0, n-1], say arr2=[0, 0, 2, 3]. How can I find the ...
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6
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1
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73
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Calculating quantiles of timeseries data and then create a "fanplot"
My code is working properly, but I am looking for better approach in the calculation of quantiles and the finding of the data in the dataframe.
...
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1
vote
1
answer
48
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Exponentially-weighted moving mean and standard deviation of an irregularly-spaced weighted time series
The following numpy/python function computes exponentially-weighted moving mean and standard deviation of an irregularly-spaced weighted time series. I want to make it faster by getting rid of the ...
- 123
3
votes
1
answer
65
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Collatz conjecture with plots
I have an assignment where I write a Collatz Conjecture program for a series of starting values from 1 to N and make two plots: number of iterations vs starting value and computed numbers vs starting ...
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1
vote
1
answer
121
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Slicing multi index DataFrame into JSON object
I have a MultiIndex pd.DataFrame that I generated from a .txt that is forecast model data.
...
- 408
0
votes
2
answers
60
views
Fastest way to find common events in 2 time series numpy arrays and calulate synchronisation statistic
Given 2 numpy arrays a1 and a2 (composed only of 0 and 1's), find index locations of all 0's in ...
- 162
1
vote
1
answer
239
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Calculate a time weighted average of a feature
I'm trying to calculate a time weighted average of a feature (feat) based on previous rows by date for a given ...
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1
vote
1
answer
97
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Calculating all combinations from arrays AND (arrays OR floats)
Context: My question comes from needing to iterate different np.arange arrays. The main motivation is to calculate all the possible combinations between the arrays, ...
- 163
2
votes
1
answer
63
views
2
votes
1
answer
43
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find max value in islands defined by other vector
I have a vector of values vals, a same-dimension vector of frequencies freqs, and a set of frequency values ...
- 255
4
votes
1
answer
72
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Path of a particle in a non-uniform B field
I have completed my project which simulates the path of a particle trapped in a device known as a magnetic mirror. I would like your thoughts and improvements on my implementation.
Here is the code:
<...
- 215
1
vote
0
answers
52
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Solving a linear system with Gaussian Elimination
I decided to implement a solver for linear systems of equations based on the gaussian elimination and reduction to upper triangular form. The gaussian elimination is quite simple to implement but the ...
- 27k
4
votes
1
answer
101
views
Function to calculate the GC content variation in a sequence
I came across this BMC Genomics paper:
Analysis of intra-genomic GC content homogeneity within prokaryotes
And I implemented some Python functions to make this available as part of a personal project.
...
2
votes
2
answers
108
views
How can I optimize this pairwise Euclidean distance search algorithm?
x and y are two-dimensional arrays with dimensions (AxN) and (BxN), i.e. they have the same number of columns.
I need to get a matrix of Euclidean distances between each pair of rows from x and y.
I ...
1
vote
1
answer
80
views
using pandas and numpy to parse dirty .csv
I'm relatively new to Python have been writing for a few months now. I've started a Pandas Numpy project that starts with parsing large and somewhat sloppy formatted textfile, its not exactly csv but ...
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2
votes
1
answer
61
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Generating a matrix with each row having normalized weights
I just asked this question over Stack Over Flow on how to improve my code and reposting it here as someone on Stack Overflow recommended this platform.
I have written two python functions and they are ...
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3
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0
answers
56
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Implementation of a crypto formula in Python
I need to implement in Python the formula in the image. The set B is a set of real numbers \$-1 \le t \le 1\$. Also, \$\mathbb{F}_2\$ is a set with the elements 0 and 1. \$y_i\$ is the \$i\$-th ...
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1
answer
155
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Implementing histogram in python
I was trying to implement my own version of matplotlib's hist function and I came up with this:
...
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0
answers
70
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Using arrays more effectively with numpy
I previously posted some code I've been working on and had a fantastic answer, but as I didn't post the full code I was then unable to bring it all together using the much faster numpy implementation, ...
- 63
2
votes
1
answer
99
views
Calculating a function over a large array
I have written some code to determine an interpolation matrix over a grid of points. I originally wrote the code in matlab, where under the specified parameters it took just over 2 minutes. The ...
- 63
0
votes
1
answer
374
views
line-circle intersection [closed]
I have this code that generates a random line and a random circle.
...
- 109
2
votes
0
answers
190
views
Python loading image into memory (numpy arrays) from database bytes field fast
I am looking for feedback on the function below to load a png image stored as bytes from a MongoDB into numpy arrays.
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13
votes
5
answers
2k
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Iterate through two arrays calculating a statistic from indexes of zeros
I write a function which takes as input 2 arrays of zeros and ones ~8000 elements per array. Input array size is variable, can have much higher number of elements. The density of ones is expected to ...
- 162
3
votes
1
answer
152
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Dynamically indexing numpy array
I want to create a function that takes a numpy array, an axis and an index of that axis and returns the array with the index on the specified axis fixed. What I thought is to create a string that ...
- 133
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0
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47
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Vectorized code to find the position and length of runs of 1s in a bit matrix
I'm trying to write something like an adjusted run-length encoding for row-wise bit matrices. Specifically I want to "collapse" runs of 1s into the number of 1s in that run while maintaining ...
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0
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44
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Vectorizing a working custom similarity function further using numpy
I am new to python, and even more new to vectorization. I have attempted to vectorize a custom similarity function that should return a matrix of pairwise similarities between each row in an input ...
- 121
2
votes
1
answer
252
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Applying Minimum Image Convention in Python
I am computing pairwise Euclidean distances for 3-D vectors representing particle positions in a periodic system. The minimum image convention is applied for each periodic boundary such that a ...
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3
votes
0
answers
42
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Nearest neighbor search algorithm of quantization
I'm doing some research on Nearest Neighbor Search of quantization, where running speed is very important. As I've just started using Python, I wonder if the following code for multi-processes can be ...
- 31