What is the most efficient way to map a function over a numpy array? The way I’ve been doing it in my current project is as follows: However, this seems like it is probably very inefficient, since I am using a list comprehension to construct the new array as a Python list before converting it … Read more
Build a new list with a list comprehension: You can modify the original list in-place if you want, but it doesn’t actually save time: Here are (Python 3.6.3) timings demonstrating the non-timesave: And Python 2.7.6 timings:
Python includes a profiler called cProfile. It not only gives the total running time, but also times each function separately, and tells you how many times each function was called, making it easy to determine where you should make optimizations. You can call it from within your code, or from the interpreter, like this: Even more … Read more
One simplistic approach to measuring the “elapsed time” between events is to just grab the current date and time. In SQL Server Management Studio To calculate elapsed times, you could grab those date values into variables, and use the DATEDIFF function: That’s just one approach. You can also get elapsed times for queries using SQL … Read more
Gcc 7.1 -O3 these are all identical, godbolt.org/z/a-hc1d – jterm Apr 25 at 3:27 Original answer: Did some digging. Below is an example program and the relevant assembly: Code: Assembly: This was compiled with -std=c++11 -O2. You can see that there is quite a lot more work for the return “”; statement and comparably little for return std::string and return {}; (these … Read more
Clearest and fastest way to do it. You can also consider using a set, but constructing that set from your list may take more time than faster membership testing will save. The only way to be certain is to benchmark well. (this also depends on what operations you require)
You can use the List.addAll() method. It accepts a Collection as an argument, and your set is a Collection. EDIT: as respond to the edit of the question.It is easy to see that if you want to have a Map with Lists as values, in order to have k different values, you need to create k different lists.Thus: You cannot avoid … Read more
Can anyone give me a good example of when CROSS APPLY makes a difference in those cases where INNER JOIN will work as well? See the article in my blog for detailed performance comparison: INNER JOIN vs. CROSS APPLY CROSS APPLY works better on things that have no simple JOIN condition. This one selects 3 … Read more
The comment was referring to the Big-O Notation. Briefly: O(1) means in constant time – independent of the number of items. O(N) means in proportion to the number of items. O(log N) means a time proportional to log(N) Basically any ‘O’ notation means an operation will take time up to a maximum of k*f(N)where: k is a … Read more
With a clustered index the rows are stored physically on the disk in the same order as the index. Therefore, there can be only one clustered index. With a non clustered index there is a second list that has pointers to the physical rows. You can have many non clustered indices, although each new index … Read more