How to code NESTED CYCLES

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pipor
pipor 2023-9-9
评论： Image Analyst 2023-9-10
f=[3 6 3 9]
b=[5 8 10 12]
a is a function with parameter f and b!
for l=1:numel(b)
for i=1:numel(f)
a(f(i),b(l))
end
end
but this is a problem:
if b is empty the function won't loop me with "f"

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采纳的回答

Star Strider
Star Strider 2023-9-9
Ran in:
I would set the empty array to 1 (so that it iterates one time only) and be done with it —
a = @(x,y) [x y];
f = [3 6 3 9]; % Neither Empty
b = [5 8 10 12];
if isempty(f)
f = NaN;
elseif isempty(b)
b = NaN;
end
for l=1:numel(b)
for i=1:numel(f)
q = a(f(i),b(l))
end
end
q = 1×2
3 5
q = 1×2
6 5
q = 1×2
3 5
q = 1×2
9 5
q = 1×2
3 8
q = 1×2
6 8
q = 1×2
3 8
q = 1×2
9 8
q = 1×2
3 10
q = 1×2
6 10
q = 1×2
3 10
q = 1×2
9 10
q = 1×2
3 12
q = 1×2
6 12
q = 1×2
3 12
q = 1×2
9 12
f = []; % 'f' Empty
b = [5 8 10 12];
if isempty(f)
f = NaN;
elseif isempty(b)
b = NaN;
end
for l=1:numel(b)
for i=1:numel(f)
q = a(f(i),b(l))
end
end
q = 1×2
NaN 5
q = 1×2
NaN 8
q = 1×2
NaN 10
q = 1×2
NaN 12
f = [3 6 3 9]; % 'b' Empty
b = [];
if isempty(f)
f = NaN;
elseif isempty(b)
b = NaN;
end
for l=1:numel(b)
for i=1:numel(f)
q = a(f(i),b(l))
end
end
q = 1×2
3 NaN
q = 1×2
6 NaN
q = 1×2
3 NaN
q = 1×2
9 NaN
The ‘default’ value (here ‘NaN’) can be any value that makes sense in the context of whatever ‘a’ does. If a given argument is added, then set it to the identity element for that operation, so if it is added set it to 0 if the associated vector is empty, if it is multiplied, set it to 1.
.

更多回答（2 个）

Bruno Luong
Bruno Luong 2023-9-9
Ran in:
Reverse the 2 loops, then it loops on f
f=[3 6 3 9]
f = 1×4
3 6 3 9
b=[]
b = []
for i=1:numel(f)
f(i)
for l=1:numel(b)
a(f(i),b(l))
end
end
ans = 3
ans = 6
ans = 3
ans = 9
  2 个评论
pipor
pipor 2023-9-9
I wrote the code in general but I don't know which array is empty..it can be f or b
Bruno Luong
Bruno Luong 2023-9-9
编辑：Bruno Luong 2023-9-9
Split in three loops if you have to
for i=1:numel(f)
for l=1:numel(b)
% ... do something with both f(i) and b(l)
a(f(i),b(l))
end
end
for i=1:numel(f)
% ... do something with f(i) ALONE
end
for l=1:numel(b)
% ... do something with b(l) ALONE
end

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Image Analyst
Image Analyst 2023-9-9
Check them in advance:
if isempty(b)
% What to do
return;
end
if isempty(f)
% What to do
return;
end
for l=1:numel(b)
for i=1:numel(f)
something = a(f(i),b(l))
end
end
  2 个评论
pipor
pipor 2023-9-9
移动：Dyuman Joshi 2023-9-9
if b=[] it don't execute cycle for
b=[];
f=[3 4 5];
if isempty(b)
% What to do
return;
end
if isempty(f)
% What to do
return;
end
for l=1:numel(b)
for i=1:numel(f)
fprintf("execure cycle \n");
end
end
Image Analyst
Image Analyst 2023-9-10
Correct. Why would you want to continue if one is empty? If you do you'll just get an error. If you can "fix" the situation, do so inside the if -- for example Star set them to nan instead. If you can't fix the situation, you should just exit the code after alerting the user.

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