Calculate values inside a nested loop with different steps and store them in the same variable.

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Ancalagon8 2022-12-8

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编辑： Ancalagon8 2022-12-17

I have a matrix (x) and want to calculate where its values are above certain thresholds and store the results in a new matrix (C). To be more specific, I need to check whether the condition sum(x>i) is met in 18 different values of i (classes). My difficulty is that I want a different step so for the first ten values step=1, while the remaining 8 while have step=5. I tried a nested loop but the result was not the expected. Any ideas how to proceed?

for i=1:10
     C(i)= sum(x>i);  
for j=15:5:50
    C(j)= sum(x>j);
end 
end

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Stephen23 2022-12-16

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编辑：Stephen23 2022-12-16

Assuming that SUM() returns a scalar:

V = [1:10,15:5:50];
C = V; % preallocate
for k = 1:numel(V) % loop over indices, not your data values
    C(k) = sum(x>V(k));
end

Note that in MATLAB it is almost always easier to iterate over indices, rather than over data values.

Or alternatively:

C = arrayfun(@(v)sum(x>v), V)

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更多回答（1 个）

Jiri Hajek 2022-12-8

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Hi, you can use any special vector of indexes (natual numbers) like this:

j = [1:10,15:5:50];
for i=j
     C(i)= sum(x>i);
end

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Ancalagon8 2022-12-16

编辑：Ancalagon8 2022-12-17

One option is to use nonzeros, but what if a value that I need is zero?

Stephen23 2022-12-16

编辑：Stephen23 2022-12-16

"your answer does not help me understand why I receive 50 values instead of 18"

Basically you are doing this:

A(50) = pi
A = 1×50
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0

How many elements do you expect an array to have, when you assign something to its 50th element?

"One option is to use nonzeros, but whati if a value that I need is zero?"

As I wrote earlier, just actual indices for indexing, not your data values.

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