Effectively, yes, it's slow because it's a nested for loop, because of the size. Python's element in list operation works by just searching the entire list, element by element, for the one it wants. If you have to do that for every single element in new, that means you're possibly searching the entire old for each element in new.
Full Answer
What is a nested loop in Python and how to use it?
In Python, a loop inside a loop is known as a nested loop. In this tutorial, we will learn about nested loops in Python with the help of examples. What is a Nested Loop in Python? When To Use a Nested Loop in Python? What is a Nested Loop in Python? A nested loop is a loop inside the body of the outer loop.
What is the slowest way to write a recursive loop in Python?
You cannot replace recursive loops with map (), list comprehension, or a NumPy function. “Dumb” code (broken down into elementary operations) is the slowest. Use built-in functions and tools.
What happens when you continue a loop in Python?
In Python, when the continue statement is encountered inside the loop, it skips all the statements below it and immediately jumps to the next iteration. In the following example, we have two loops. The outer for loop iterates the first list, and the inner loop also iterates the second list of numbers.
How long does it take to calculate three nested for loops?
These are only examples; in reality the lists contain hundreds of thousands of numbers. The interpreter takes tens of seconds to calculate the three nested for loops. Is it possible to somehow speed up this code, e.g. using itertools or any other module/function?
Are nested for loops slow in Python?
Using Pure Python We can see that in the case of nested loops, list comprehensions are faster than the ordinary for loops, which are faster than while.
Are nested for loops slow?
Nested loops can get difficult to understand relatively quickly, though some nesting of loops is fine - providing, as others point out, that doesn't mean you're creating a performance issue by using an extremely (and unnecessarily) slow algorithm.
Are nested for loops faster?
HOWEVER, the conclusion is CONSISTENT: The nested loop is much FASTER. When the iteration time is 100^5, the difference is significant: 321.49 vs 210.05. There is about 1.53-time gap between them. Generally, we don't face this kind of long iteration, I'm just curious to know reason of the anomalistic situation.
How can we reduce the time complexity of nested for loop?
With regard to reducing the time complexity of O(n²) squared, we can work to reduce to O(n) linear or O(log(n)) in most cases, which would make our algorithm to perform faster. There are some category of problems where it's not possible to reduce in optimal ways, but in our example it's perfectly possible to reduce.
Can nested loops cause performance issues?
Nested Loops can greatly reduce the innovative potential of the code because it negatively impacts performance.
Is 3 nested for loops bad?
It's a practice to avoid as much as possible because the number of nested loops and efficiency are directly connected. If you have 1 nested loop complexity of algorithm is on average O(n)2 and 2 nested loops complexity increase to O(n)3.
How many nested for loops is too many?
Microsoft BASIC had a nesting limit of 8. @Davislor: The error message refers to the stack size in the compiler, which is also a program, and which is recursively processing the nested-looped construct.
How do I make my for loop faster?
Make it faster by serializing/caching your result so you don't have to recalculate it every time you run the program.
Which is the fastest loop in Python?
I think the answer here is a little more subtle than the other answers suggest, though the gist of it is correct: the for loop is faster because more of the operations happen in C and less in Python.
How do you reduce the time complexity of a for loop in Python?
Also, you can just iterate till square root of the Number, instead of looping till number itself, thereby reducing time complexity exponentially.
What is the time complexity for a nested for loop?
The time complexity of nested loops is equal to the number of times the innermost statement is executed.
What is the time complexity of 3 nested for loop?
+n iterations n*(n+1)/2 which is O(n2) .
Array initialization
needs 24 GB of RAM (integers) and takes 3:28 minutes on my PC. Whereas
Random samples
did not work for me, so I replaced it and increased k for more stable measurements
The loop
The loop will need most work, since you'll avoid Python loops in Numpy whenever possible.
Code and analysis
Now, as we have the algorithm, we will compare several implementations, starting from a straightforward one. The code is available on GitHub.
Takeaways
Do numerical calculations with NumPy functions. They are two orders of magnitude faster than Python’s built-in tools.
What is a nested loop in Python?
A nested loop is a part of a control flow statement which helps you to understand the basics of Python.
What is a break statement in a nested loop?
Break Nested loop. The break statement is used inside the loop to exit out of the loop. If the break statement is used inside a nested loop (loop inside another loop), it will terminate the innermost loop. In the following example, we have two loops.
How many times does an inner loop execute?
The inner for loop will execute ten times for each outer number. In the body of the inner loop, we will print the multiplication of the outer number and current number. The inner loop is nothing but a body of an outer loop. Python nested for loop.
How many numbers does the outer for loop iterate?
The outer for loop iterates the first four numbers using the range () function, and the inner for loop also iterates the first four numbers. If the outer number and a current number of the inner loop are the same, then break the inner (nested) loop. Example:
How does the continue statement work in Python?
In Python, when the continue statement is encountered inside the loop, it skips all the statements below it and immediately jumps to the next iteration.
Can an outer loop have more than one inner loop?
The outer loop can contain more than one inner loop. There is no limitation on the chaining of loops. In the nested loop, the number of iterations will be equal to the number of iterations in the outer loop multiplied by the iterations in the inner loop.
Can you use a while loop inside a for loop?
While loop inside a for loop. Its is very common and helpful to use one type of loop inside another. we can put a while loop inside the for loop. Assume we wanted to repeat each name from a list five times. Here we will iterate the list using an outer for loop.