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Inconsistent behaviour in fprintf output (scripts and LiveScripts)?

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John
John on 12 Mar 2021
Commented: Adam Danz on 24 Mar 2021
The output from fprintf seems to be inconsistent when called from within a livescript. The interpreter seems to be adding extra newlines after each call.
For example take the following code:
K = 10;
for k=1:K
fprintf('Count: %d',k);
if k < K
fprintf(', '); %Add a comma for all but the last number
end
end
fprintf('\n')
If you execute this code in a standard script, the output is formatted correctly:
Count: 1, Count: 2, Count: 3, Count: 4, Count: 5, Count: 6, Count: 7, Count: 8, Count: 9, Count: 10
If executed in a LiveScript, the output looks much different:
Count: 1
,
Count: 2
,
Count: 3
,
Count: 4
,
etc.
Is there a way to supress these extra newlines? Is this intended behaviour? Is there an elegant way of getting around this? (I could assemble the output string, before calling fprintf, but that seems cumbersome)

Accepted Answer

Adam Danz
Adam Danz on 24 Mar 2021
Edited: Adam Danz on 24 Mar 2021
I agree that the behavior in LiveEditor is inconsistent.
This version is better though still displays the final text on a separate line in LiveEditor.
K = 10;
for k=1:K
if k < K
fprintf('Count: %d, ',k)
else
fprintf('Count: %d\n',k)
end
end
Count: 1, Count: 2, Count: 3, Count: 4, Count: 5, Count: 6, Count: 7, Count: 8, Count: 9,
Count: 10
> Is there an elegant way of getting around this
Yes. The loop itself is not very elegant even when it works.
Although the function you shared is probably a simplified example of what you're actually doing, a much more elegant approach that works in command window, m-files, and in LiveEditor is this single line that doesn't rely on a loop.
disp(strjoin(compose('Count: %d',1:K),', '))
Count: 1, Count: 2, Count: 3, Count: 4, Count: 5, Count: 6, Count: 7, Count: 8, Count: 9, Count: 10
  2 Comments
Adam Danz
Adam Danz on 24 Mar 2021
Glad to hear it. The compose and strjoin functions are quite common but I can see how it's less readable than a simple fprintf command.

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More Answers (1)

Ramnarayan Krishnamurthy
Ramnarayan Krishnamurthy on 24 Mar 2021
To get the same output for this example as in the command window, one possible approach is to wrap your code inside a function. Here is an example live script:
test(10)
function test(K)
% your code here
for k=1:K
fprintf('Count: %d',k);
if k < K
fprintf(","); %Add a comma for all but the last number
end
end
fprintf('\n')
end
HTH
  2 Comments

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