Write to file inside a loop

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Ali Rafiei
Ali Rafiei on 2 Jul 2019
Commented: Rik on 4 Jul 2019
I have a loop that each time generates a value 'b1'. I want to create a matrix of all the b1 values to make a histogram at the end. The code that I found is:
q = b1;
this code overwrites and only the last b1 is saved on pqfile. wondering if anyone can help me not overwrite
  1 Comment
Rik on 4 Jul 2019
@Ali, did either answer solve your issue? If so, please consider accepting the answer that works best for you, or comment with your remaining questions.

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Answers (2)

infinity on 2 Jul 2019
Edited: Rik on 2 Jul 2019
You can refer a simple solution as follows
saveb1 = [];
for (your loop)
your code to compute b1;
saveb1 = [saveb1; b1];
In this method, you will save b1 of each loop to a varible saveb1. After the loop, you can save "saveb1" to the text file.

Rik on 2 Jul 2019
Or a much better practice: if you know the number of iterations you should pre-allocate your output array.
saveb1 = zeros(1,k);
for n=1:k
%your code to compute b1 goes here
Alternatively, if you insist of using a file write:
%prepare an empty file
if fid==-1
error('file could not be opened')
for n=1:k
%your code to compute b1 goes here
And now you can read the file with all the b1 values.
Rik on 2 Jul 2019
Yes it would. There might be more efficient options, but simply pasting the code that generates a value for b1 for a given value of n into that loop should do the trick. If it is a slow process you could use the file write (or a normal save/load) to check which values have already been calculated and fill those empty slots.

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