Combining Multiple for Loops into Single Iterator

Combining multiple for loops into single iterator

Since you care about performance, you should forget about combining iterators for the foreseeable future. The central problem is that compilers cannot yet untangle the mess and figure out that there are 3 independent variables in it, much less perform any loop interchange or unrolling or fusion.

If you must use ranges, use simple ones that the compiler can see through:

for (int const x : boost::irange<int>(xstart,xend))
for (int const y : boost::irange<int>(ystart,yend))
for (int const z : boost::irange<int>(zstart,zend))
function_doing_stuff(x, y, z);

Alternatively, you can actually pass your functor and the boost ranges to a template:

template <typename Func, typename Range0, typename Range1, typename Range2>
void apply_ranges (Func func, Range0 r0, Range1 r1, Range2 r2)
{
for (auto const i0 : r0)
for (auto const i1 : r1)
for (auto const i2 : r2)
func (i0, i1, i2);
}

If you truly care about performance, then you should not contort your code with complicated ranges, because they make it harder to untangle later when you want to rewrite them in AVX intrinsics.

How to combine multiple for loops into a single generator python

This is itertools.product:

import itertools
for year, month, hour, node in itertools.product(
yearsindex, monthindex, hourindex, nodeindex):
dosomething(year, month, hour, node)

You can see that cramming all that onto a single logical line isn't really a readability improvement. There are several ways to make it an improvement. For example, if you can avoid unpacking the tuples the iterator gives you, or if you can put the arguments to itertools.product in a list and unpack them with *args:

for arg_tuple in itertools.product(*indexes):
dosomething(*arg_tuple)

If the loop body is longer than just one line of dosomething, you also get the benefit of decreased indentation. With a short loop body, that doesn't matter much.

Merge the code from 2 for-loops into 1 for-loop

You can put everything in a list, which will consume a bit more space:

for walk, turn in [(0,-72),(71,108),(71,0)]*10+[(29,90),(73,72),(73,90),(29,72)]*10:
fd(walk)
rt(turn)

Merge two for-loops into one for-loop

Based on given answers, the best way to redesign the code is this:

num = 224

list1 = [i for i in range(2, num) if num % i == 0]

if list1:
print(num, 'is not prime and can be divided by the following numbers:\n', list1)
else:
print(num, 'is Prime.')

Thank you @matthieu-brucher and @blhsing

Combining multiple for loops that iterate over matrix python

So assuming a correct value is a value greater than 1, i did this: Also to have infinite values, i organized the results in a dictionary:

matrix = [
["", "article1.txt", "article2.txt", "article3.txt"],
["ink", 2, 3, 0],
["mouse", 0, 2, 1],
["rat", 0, 0, 1]]
results = {product[0]: [1 for a in product[1:] if a > 0].count(1) for product in matrix[1:]}

print(results)

I hope this is what you expected. Let me know if you need any adjustments or explanations. This would be the result for your example:

{'ink': 2, 'mouse': 2, 'rat': 1}

Combining many for loops into one

The following function does the job but it will be slower then the original code

function loop(f, args, varargin)
if ~isempty(args)
for arg = args{1}
loop(f, args(2:end), varargin{:}, arg);
end
else
f(varargin{:});
end

You can start your calculation with

loop(@J, {1:10, 2:15, 3:5, 7:9});

How to combine two FORs into one

You need to compute the row and column from a single index, then:

for(int i = 0; i < 5 * 5; i++)
{
int row = i / 5;
int column = i % 5;
x[row][column] = rg.nextInt();
}

The use of / and % is classic, here: as you iterate over the indices of the matrix, the division is used to figure out which row you're on. The remainder (%) is then the column.

This gorgeous ASCII art shows how the 1-dimensional indices are located in the 2D matrix:

 0  1  2  3  4
5 6 7 8 9
10 11 12 13 14
15 16 17 18 19
20 21 22 23 24

It should be clear that for any value in the first row, that value divided by 5 is the row index itself, i.e. they're all 0.

How to combine two for loops

You need the itertools.chain():

Make an iterator that returns elements from the first iterable until it is exhausted, then proceeds to the next iterable, until all of the iterables are exhausted.

from itertools import chain

for x in chain(range(0, 26), range(75, 101)):
print(x)

Works for both Python 2 and 3.

Pythonic way to combine two FOR loops and an IF statement?

Is there a way to write it in one line

Yes.

or in a Pythonic way?

What you have currently is already the most Pythonic way, no need to change anything here.



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