MATLAB Answers

How to update variable names after a "clear"

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Robin H
Robin H on 17 Oct 2017
Commented: Jan on 19 Jul 2019
Dear Community,
I wonder if there is another way to clear variables. If I do:
clear var1 var2
% or
The variables are strings or purple and are not updated if the name of the variable is changed.
How can I realize that variables after a clear or clearvars are updated if the variable name is changed. (e.g. the original variable name was not descriptive enough).
Edit: I mean not during running the code, the variable name is not dynamic! I mean during writing, the editor offers you the possibility to rename all instances of a variable (Shift-Enter)
>> Press Shift+Enter to rename 4 instances of " var1" to " anothernameOfVar1"
within a script. Variables after a clear or clearvars are not affected by this.
Best, Robin


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Jan on 17 Oct 2017
After a clear x, the variable "x" is not longer existing. Then it would be meaningless if the editor changes later occurrences. This is a logical behavior:
x = 19
clear x
x = 'hello'
Now renaming the initial x should stop after the 2nd line.
Rik on 17 Oct 2017
Except that this isn't how it works (at least in R2017b). ALL occurrences of x are replaced, except for the occurrence as a string (either in exist or clear)
Guillaume on 17 Oct 2017
@Jan, you'd have a point if that is what was happening. Unfortunately, the automatic renaming is indeed broken. Just tested the following (R2017b online):
x = 5;
a = x;
clear x %unnecessary clear
x = 10;
b = x;
Then renamed the first x to y and pressed shift+enter for automatic renaming and ended up with
y = 5;
a = y;
clear x %unnecessary clear
y = 10;
b = y;
So it renames all instances of x regardless of whether or not they're actually the same variable but doesn't rename it in the clear call.
The reason is most likely because in that call x is actually the char array 'x' (since this is the command form of clear) and automatic renaming does not look in strings (or comments for that matter).

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Accepted Answer

Guillaume on 17 Oct 2017
Edited: Rik on 17 Jul 2019
Unfortunately, this is a limitation of matlab's editor.
Note that
clear x
is exactly the same as
The former is the command form of the latter. In both cases, the input to clear is the char array 'x'.
The automatic renaming does not look in char arrays, strings or comments. So as Rik commented, the only way to deal with that is by doing the renaming yourself.
Matlab refactoring tools have thankfully improved over the years but are still way behind what is available in other editors (It really pales when compared to Visual Studio).

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Robin H
Robin H on 17 Oct 2017
I mark this answer, even though it is not the solution due to the limitations of the editor. Might be irrelevant in a future release.
Thanks all

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More Answers (1)

Jan on 17 Oct 2017
Edited: Jan on 17 Jul 2019
Clearing variables is rarely useful in Matlab, but a waste of time only. So on one hand it is not exactly clear, what you are asking for, but take into account to simply remove this line.


Robin H
Robin H on 17 Oct 2017
I made a edit on my question to make more clear hopefully.
I mean during writing Matlab editor offers you to rename all instances of a variable (Shift-Enter) once you change the name. Variable names after a clear (or "exist" as Rik pointed out) are not affected by this.
Stephen Cobeldick
Stephen Cobeldick on 17 Oct 2017
@Robin H: Note that the variables after clear are different variables, because after clear that new variable (likely) uses a different memory location and (likely) contains different data. The fact that you have coincidentally used the same name is irrelevant.
Jan on 19 Jul 2019
@Robin H: I understood. And if you want to replace all occurences, you can use NotePad++. I've written a Matlab function to replace strings in M-files. It is a little bit tricky to distinguish quoted and double quoted strings from names of variables, but not magic. I avoid te non-functional form of commands like clear x, but I do not have any needs for clear commands at all.

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