performance
How to capture multiple camera streams with OpenCV?
To capture multiple streams with OpenCV, I recommend using threading which can improve performance by alleviating the heavy I/O operations to a separate thread. Since accessing the webcam/IP/RTSP stream using cv2.VideoCapture().read() is a blocking operation, our main program is stuck until the frame is read from the camera device. If you have multiple streams, this … Read more
Roll rows of a matrix independently
Sure you can do it using advanced indexing, whether it is the fastest way probably depends on your array size (if your rows are large it may not be): rows, column_indices = np.ogrid[:A.shape[0], :A.shape[1]] # Use always a negative shift, so that column_indices are valid. # (could also use module operation) r[r < 0] += … Read more
Analyzing Code for Efficiency?
INSERTED: Let’s look at “statistical significance”. Assume there’s a function call instruction somewhere. You can’t necessarily see it – a class, or a macro, or the compiler, may have slipped it in. There are other calls to the same function nearby, but this call is in a loop, or its arguments are such as to … Read more
What is the performance impact of non-unique indexes in pandas?
When index is unique, pandas use a hashtable to map key to value O(1). When index is non-unique and sorted, pandas use binary search O(logN), when index is random ordered pandas need to check all the keys in the index O(N). You can call sort_index method: import numpy as np import pandas as pd x … Read more
Java lambdas 20 times slower than anonymous classes
You are obviously encountering the first-time initialization overhead of lambda expressions. As already mentioned in the comments, the classes for lambda expressions are generated at runtime rather than being loaded from your class path. However, being generated isn’t the cause for the slowdown. After all, generating a class having a simple structure can be even … Read more
Opening/closing tags & performance?
3 simple rules for you to get it right: No syntax issue can affect performance. Data manipulation does. Speak of performance only backed with results of profiling. Premature optimization is the root of all evil Performance issues are quite hard to understand. It is advised for the newbies not to take it into account. Because … Read more
Good ways to improve jQuery selector performance?
There is no doubt that filtering by tag name first is much faster than filtering by classname. This will be the case until all browsers implement getElementsByClassName natively, as is the case with getElementsByTagName.
Timertask or Handler
Handler is better than TimerTask. The Java TimerTask and the Android Handler both allow you to schedule delayed and repeated tasks on background threads. However, the literature overwhelmingly recommends using Handler over TimerTask in Android (see here, here, here, here, here, and here). Some of reported problems with TimerTask include: Can’t update the UI thread … Read more
Does setting Java objects to null do anything anymore?
It depends a bit on when you were thinking of nulling the reference. If you have an object chain A->B->C, then once A is not reachable, A, B and C will all be eligible for garbage collection (assuming nothing else is referring to either B or C). There’s no need, and never has been any … Read more