Find elemet which are satisfy given condition

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Mariia
Mariia 2023-3-14
编辑： Dyuman Joshi 2023-3-14
hello to everyone! I have a task, where i need to find in column (x) with 100 numbers, such values which are less or equal than 400. And write all these values in new created matrix x1. When I run this code - new matrix from zeros is created, but it doesn't contain any numbers. What could be the reason? Will appreciate your help!
x1=zeros(100,1);
for i=1:100
if x(i)<=400
x1(i)=x(i);
end
end
  1 个评论
Dyuman Joshi
Dyuman Joshi 2023-3-14
编辑：Dyuman Joshi 2023-3-14
Ran in:
Your code looks good. What is the value of variable x?
You can assign the values via indexing, which is more efficient than loop
x = randi(750,10,1)
x = 10×1
386 629 86 13 279 497 411 409 239 458
x1 = zeros(size(x));
idx = x<=400;
x1(idx) = x(idx)
x1 = 10×1
386 0 86 13 279 0 0 0 239 0

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采纳的回答

Jan
Jan 2023-3-14
Ran in:
Your code is working:
x = [1, 401, 400, 500, 10, 300];
x1 = zeros(numel(x), 1);
for i = 1:numel(x)
if x(i) <= 400
x1(i) = x(i);
end
end
x1.'
ans = 1×6
1 0 400 0 10 300
You can omit the zeros also:
x = [1, 401, 400, 500, 10, 300];
x1 = zeros(numel(x), 1);
k = 0; % Another counter
for i = 1:numel(x)
if x(i) <= 400
k = k + 1;
x1(k) = x(i);
end
end
x1 = x1(1:k); % Crop unused elements
A more Matlab'ish way is to omit the loop:
x1 = x(x <= 400) % Logical indexing

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