35
votes
Accepted
Scale Numpy array to certain range
NumPy provides numpy.interp for 1-dimensional linear interpolation. In this case, where you want to map the minimum element of the array to −1 and the maximum to +1,...
- 49.6k
32
votes
Accepted
Looking for a way to create a particular matrix in python in a less amount of time
The NumPy Reference should be the first place you look when you have a problem like this. The operations you need are nearly always in there somewhere. And functions that you find while browsing the ...
- 49.6k
31
votes
Python decibel meter-accurate?
Indent your code with a PEP8-compliant IDE or linter; it's a perfect mess right now.
Move your global code into functions and maybe classes. There are two good use cases for classes here - one for a ...
- 59.1k
29
votes
Accepted
Crop black border of image using NumPy
Vectorization with NumPy
When read with cv2.imread or skimage.io.imread or scipy.misc.imread,...
- 896
25
votes
Accepted
Remove points in a straight line
A look at the second plot in the post shows that something has gone wrong. There are four points in a line here:
This shouldn't be possible, since "points that create a straight line when plotted" ...
- 49.6k
23
votes
22
votes
Crop black border of image using NumPy
As you've discovered, looping over individual pixels in Python is very slow. You need to organize your computation so that it uses a series of NumPy (or SciPy, or Scikit-Image, or OpenCV) operations ...
- 49.6k
18
votes
Accepted
Remove pixel patch in image which is stored as array
On my computer it takes 1.745 seconds to run the code in the post.
There's no need for the array of random indexes to be two-dimensional:
...
- 49.6k
18
votes
Accepted
Iterate through two arrays calculating a statistic from indexes of zeros
First, some basics of your implementation:
Type-hint your arguments; I had to read and investigate a bunch to deduce that tau is a positive integer
...
- 59.1k
16
votes
Accepted
Comparing pixels against RGB value in NumPy
Your original code can be rewritten as:
mask = np.all(img == (255, 127, 63), axis=-1)
It is a little cleaner, but not more efficient, as it still has to allocate ...
- 6,562
14
votes
13
votes
Accepted
Python program that draws the Mandelbrot set fractal
The key thing to remember when working with numerical code is that the CPython interpreter is pretty slow (it trades speed for flexibility) and so you must avoid running in the interpreter whenever ...
- 49.6k
13
votes
Accepted
Processing an image to extract green-screen mask
There's a simpler way to create the empty image using numpy.zeros_like:
empty_img = numpy.zeros_like(img)
As Austin Hastings ...
- 303
12
votes
Accepted
Recursively Save Python Dictionaries to HDF5 Files Using h5py
Here's what I tested.
I took out the classmethod stuff to make it easier to read, and simplified names a bit. I'll defer judgement on whether that stuff is needed as part of a larger package or not.
...
- 1,481
12
votes
Accepted
Optimize Performance of Region Checking in List Comprehension
Loops over large arrays are not really a good idea in Python. This is why your original list comprehension is not terribly fast.
Your numpy version is loop free, but as far as I know, ...
- 7,234
12
votes
Accepted
How to clean the indexes, and ideally not create an additional array
Here is a review of the solution.
^ is xor in Python. It is not for computation of exponentials.
When running code outside a method / class, it is a good practice ...
- 2,321
11
votes
Generate sample coordinates inside a Polygon
Rejection sampling was proposed in comments on the other answer. The problem with rejection sampling is that the area of a polygon can be an arbitrarily small fraction of its bounding box, for example:...
- 49.6k
11
votes
Accepted
Combining two clock tick vectors with NumPy
Everything apart from the for loop in your code is already vectorized which leaves only the for loop to be optimized.
You ...
- 226
11
votes
Accepted
Plot timings for a range of inputs
matplotlib adding stuff to the current figure is because you are not using the OO-interface. It is slightly clunkier, but allows way more freedom
In my view, you ...
- 9,100
11
votes
Accepted
Table of Tribonacci sequence using NumPy and PANDAS
You’re using the wrong tool for the job. Basically, you do all the computation in Python, use numpy for intermediate storage and ...
- 28.6k
11
votes
Accepted
Solve the phase state between two haplotype blocks using markov transition probabilities
Before we get to the interesting stuff, we should handle some stylistic niggles. Note that PEP 8 is a de-facto style for Python code. First, imports should be sorted
...
- 9,593
11
votes
Remove points in a straight line
You can use Ramer Douglas Peuker algorithm. RDP takes a curve and eliminates points that are close to straight lines. It is distance based. Starting with the two endpoints, it forms a line and picks ...
- 543
10
votes
Accepted
Game of Life with NumPy
That next_state function creates two brand new numpy array. Creating numpy array is slow. Should just update an existing numpy array.
Can divide the code into two ...
10
votes
Modifying Titration Data analysis results
I've never used numpy or matplotlib, so I can only speak to issues of style.
You're allowing for far too much nesting here. Your code consists of a giant, dense, deeply nested chunk. As a result, the ...
- 16.2k
10
votes
Iterate through two arrays calculating a statistic from indexes of zeros
for x,y in product(event_index1,event_index2) looks like an efficiency killer. If the lengths of event_index1, event_index2 are <...
- 55.9k
9
votes
Accepted
Calculating a table of deBroglie wavelengths for various electron energies
First, simplify: factor out \$C^4\$ out of square root:
\$\lambda(E_k) = h\left/C\sqrt{(\frac{E_k}{C^2}+m_e)^2-m_e^2}\right.\$
Simplify even more: factor out \$m_e^2\$:
\$\lambda(E_k) = h\left/C ...
- 55.9k
9
votes
Calculating time deltas between rows in a Pandas dataframe
Use the diff().
x['time_delta'] = x.timestamp.diff().fillna(x['time_delta'])
This works as below, in a simpler example.
You could use the ...
- 91
9
votes
Accepted
Deep Neural Net implementation in Python3
The not so arbitrary Network
Your original claim was that your network is "arbitrary". From what I see, I would tend to say that it's not so arbitrary as one might expect.
Arbitrary:
number of ...
- 7,234
9
votes
Generating large testing datasets
There are already tools for choosing elements from a collection with some given probabilities. In the standard library there is random.choices, which takes the ...
- 40.9k
9
votes
Looking for the particles that are emitted when a fish is detected in Terraria
However, the entirety of the code is in 1 function and is kind of hard to read.
Agreed. And while this is not a major problem for short pieces of code like this, it will turn into a major ...
Mast♦
- 13.1k
Only top scored, non community-wiki answers of a minimum length are eligible