# How to specify a stop criterion in an if loop.

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Lewis Waswa on 3 Jul 2021
Commented: Lewis Waswa on 9 Jul 2021
I have two files named TData (j) (technical Data) and RData (i) in an array format. I also have a file NFile (i), which is supposed to specify an operation condition as follows. If an index of NFile is greater than 1, we define a newfile, NewRData (i) as the value of TData (j) that is IMMEDIATELY less than or equal to RData(i).
I have written the following code and the code seems to stop at the last value of the TData instead of the immediate less value of TData.
RData =[0.443 0.641 0.641 0.641 0.641 0.641] % 6 by 1 column matrix
NFile= [0.93 0.95 0.97 0.99 1.02 1.01] % 1 by 6 row matrix
TData =[1.2 0.87 0.64 0.44 0.32 0.25 0.21] % 7 by 1 column matrix
for i=1:size(RData,1)
for j=1:size(TData,1)
if NFile(i)>1
if TData(j)<RData(i)
NewRData(i)= TRData(j)
else
NewR(i)=R(i)
end
end
end
based on the above file, my NewR should be [0.443 0.641 0.641 0.641 0.44 0.44]
However my program give NewR as [0 0 0 0 0.21 0.21]. Kindly help me trouble shoot it. What am I missing?
dpb on 3 Jul 2021
I can't follow how, specifically, you get the result you claim is the right answer in the original Q?
IF is not a looping construct is, it seems to me, the first major conceptual problem here; the use of a double loop over i,j causes the stepping through the two vectors to go through the second, inner loop each time for each element of the outer -- that, since there is only one element being stored for each index, causes the previous N-1 loops of the outer loop to be overwritten by the results of the last.
I think need to back up to the problem definition and clarify just exactly what it is that is the actual condition being looked for -- if it is the thing about NFILE>1 is one result and <=1 another, looks to me like logical addressing could solve the problem without looping.
But, need the actual conditions to be clearly and unambiguously defined as to the desired result first before can write any algorithm.
Lewis Waswa on 9 Jul 2021
@Walter Roberson, indeed. All I needed was a break after line seven and did not have to use the initializer. Thank you

Image Analyst on 3 Jul 2021
Assuming your code is otherwise correct, you'll need to use the break command twice : once to break out of the inner loop, and then once out of that, again to break out of the outer loop:
abort = false; % Clear flag.
for i=1:size(RData,1)
for j=1:size(TData,1)
if NFile(i)<1
NewRData(i)=R(i)
elseif NFile(i)>1
if TData(j)<RData(i)
NewRData(i)= TRData(j)
i=1
% Break out of the j loop (but not the i loop);
abort = true; % Set flag indicating we need to quit both loops.
break;
end
end
end
% Now check if we need to break out of the i loop:
if abort
break; % break out of the i loop.
end
end
Lewis Waswa on 9 Jul 2021
Thank you. This worked with a bi of tweaking.

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