How to change specific numbers to 0
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So here is my current code:
A = [ 1 2 3 4 5 6 7 8 9];
B = [ 1 2 3 4];
A(~B)=0;
disp(A);
Basically I want A to be equal to [ 1 2 3 4 0 0 0 0 0 ]. But for some reason it won't take ~B, where as it will work when it is just B. Anyone know a solution to this or why this is the case? Thanks in advance!
2 Comments
Stephen23
on 17 Jun 2023
"But for some reason it won't take ~B, where as it will work when it is just B. "
Compare:
B = [1,2,3,4]
~B
The first is a numeric array, the second is a logical array. Now revise what kind of indexing MATLAB supports:
Accepted Answer
Daniel
on 17 Jun 2023
There are two ways you can select elements of an array in MATLAB.
- Pass in an array of valid indices. "Valid" means that they're within the range of indices to the array.
- Pass in an array of logical values, of the same size as the array.
a = (1:10)*2; % Demo array. This has 10 elements, indexed 1 through 10, values 2, 4, 6, ... 20.
% First method
a(1)
a(10)
a(end) % Special case: "end" refers to the last element in the array
a([5 7 2])
% Second method
mod(a,4) == 0 % Notice that this returns a "logical" data type at the output, as will any comparison
a(mod(a,4)==0)
~ is a logical operator, so ~B is an array of logicals. Since it's a logical array, it has to have the same size as A, which it doesn't. Therefore the line of code fails.
One alternative method would be to write:
A(5:end) = 0;
That will select and modify elements 5 through 9 (the last element) of A.
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More Answers (1)
John D'Errico
on 16 Jun 2023
Edited: John D'Errico
on 16 Jun 2023
For some reason? Learn to use ismember instead. What you think makes sense does not work in MATLAB. And that means you need to start back with the tutorials, to learn MATLAB syntax. Sorry. Time to start at the beginning.
2 Comments
Daniel
on 17 Jun 2023
Regarding starting at the beginning, speaking as a MathWorker, you probably have access to some MATLAB fundamentals courses if you go to matlab.mathworks.com through your university account and click on "Online Training". You may find the MATLAB Onramp and/or MATLAB Fundamentals to be helpful.
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