# How to create a loop with unknown number of iterations?

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Ivan Mich on 3 Nov 2022
Edited: Jan on 5 Nov 2022
I would like a help about a script. I have a file with three columns, each of them are numbers. I would like to satisfy a condition via a loop.I want, based on a specific equation/relationship:
in order to get only the elements from the file that satisfy this equation and not get an "emplty" file.
If not, then the relationship should be converted to
One again not then the relationship should be converted to
One again not then the relationship should be converted to
etc
I have tried the following commands:
clc
clear
filename1= 'mydata.txt';
[d1,tex]= importdata(filename1);
y_input=d1.data(:,2);
x_input=d1.data(:,1);
z_input=d1.data(:,4);
y_B=selected(:,2);
x_B=selected(:,1);
z_input_B=selected(:,4);
fin=max(z_input);
if isempty(z_input_B)
end
if isempty(z_input_B)
end
if isempty(z_input_B)
end
I need something in (i) that takes values from 0 to whatever is needed to satisfy the relation/condition and not get an "empty" file.
I mean something like
##### 2 CommentsShow 1 older commentHide 1 older comment
Ivan Mich on 3 Nov 2022
Yes it is defined before loop

Jan on 3 Nov 2022
Edited: Jan on 3 Nov 2022
k = 1;
mask = z_input < fin & z_input >= (fin - k);
else
k = k + 1;
end
end
But remember, that the value of min(z_input - fin) should help to find k directly without using a loop.
Another option is using maxk(z_input, 2) to get the 2 largest outputs, which let you determine k also.
Jan on 5 Nov 2022
Edited: Jan on 5 Nov 2022
@Ivan Mich: You ignore my answer and my comments. I have mentioned, that you modify mask , but check for isempty(z_input_B).
Checking a binary mask by isempty will fail also, because this counts the number of elements without considering their values. Look in the code I've posted: any(x) does something different from isempty(mask).
Posting an example file is not useful, because I cannot guess, what I should do with this file.
My code does already, what you have asked for and you explain repeatedly, that another code does not work. Even if I mention the problem of the other code, you do not react. So I repeat another time, that a loop is a waste of time only, because maxk(z_input, 2) reveals the value of k directly: It replies the 2 largest values and you have to subtract them only.
I've posted some code, which is working as far as I can see, and mentioned a much more efficient solution. I do not see, how I could help you further. Why do you hestitate to use these information?

Jim Riggs on 3 Nov 2022
Edited: Jim Riggs on 3 Nov 2022
What you are describing sounds like a "while" loop.
You specify a logical condition which will terminate the loop
i=0;
condition=false;
while condition == false
...
...
i=i+1;
condition = % set your termination condition
end
Ivan Mich on 5 Nov 2022
Thank you, but I actually not works...
I have tried the following commands:
k = 0;
if isempty(z_input_B)
else
k = k + 1;
end
end
but matlab crashed (I mean that do not stop executing). What I type wrong? I am absolutely sure that I have a mistake in syntax...