How to create a loop with unknown number of iterations?

27 views (last 30 days)
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:
mask = z_input<fin & z_input>=(fin-1);
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
mask= z_input<(fin-1) & z_input>=(fin-2);
One again not then the relationship should be converted to
mask= z_input<(fin-2) & z_input>=(fin-3);
One again not then the relationship should be converted to
mask= z_input<(fin-3) & z_input>=(fin-4);
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);
mask = z_input<fin & z_input>=(fin-1);
selected= d1.data(mask,:);
y_B=selected(:,2);
x_B=selected(:,1);
z_input_B=selected(:,4);
fin=max(z_input);
if isempty(z_input_B)
mask= z_input<(fin-1) & z_input>=(fin-2);
selected = d1.data(mask,:);
end
if isempty(z_input_B)
mask= z_input<(fin-2) & z_input>=(fin-3);
selected = d1.data(mask,:);
end
if isempty(z_input_B)
mask= z_input<(fin-3) & z_input>=(fin-4);
selected = d1.data(mask,:);
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
mask= z_input<(fin-i) & z_input>=(fin-(i+1));
Could you please help me?

Answers (2)

Jim Riggs
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
  5 Comments
Ivan Mich
Ivan Mich on 5 Nov 2022
Thank you, but I actually not works...
I have tried the following commands:
ready = false;
k = 0;
while ~ready
mask= z_input_B<(fin-k) & z_input>=(fin-(k+1));
if isempty(z_input_B)
ready = true;
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...
Could you please help me??

Sign in to comment.


Jan
Jan on 3 Nov 2022
Edited: Jan on 3 Nov 2022
ready = false;
k = 1;
while ~ready
mask = z_input < fin & z_input >= (fin - k);
if any(mask)
ready = true;
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.
  4 Comments
Jan
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?

Sign in to comment.

Categories

Find more on Loops and Conditional Statements in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by