When is the renamevars function introduced?

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alpedhuez 2021-8-5

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https://ww2.mathworks.cn/matlabcentral/answers/893092-when-is-the-renamevars-function-introduced

编辑： DGM 2021-8-11

I use MATLAB Version: 9.7.0.1190202 (R2019b) and got "error using eval. unrecognized function or variable 'renamevars'. Can it be that renamevar function was introduced after 2019b?

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Image Analyst 2021-8-5

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https://ww2.mathworks.cn/matlabcentral/answers/893092-when-is-the-renamevars-function-introduced#answer_761792

R2020a

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DGM 2021-8-6

编辑：DGM 2021-8-8

在 MATLAB Online 中打开

when.m

For what it's worth, there is a tool on the File Exchange called when(). In theory, it does what you want, looking up the release version a given function was introduced. The theory isn't quite the same as reality though. There are three problems with it.

1: When() relies on the web docs to get the date. It expects a particular structure to the page which has changed since the function was last updated. I've already notified the author with a fix, but have yet to see a fixed version.

2: When() will only look up things that it determines are Matlab functions. This means that it simply doesn't even try to look up functions which don't exist in the version you're using, even if the webdocs do exist.

3: The assumptions that when() uses to determine the webdocs URL aren't always correct. It assumes that the url is

url = ['https://mathworks.com/help/matlab/ref/' fname '.html'];

url = ['https://mathworks.com/help/simulink/slref/' fname '.html'];

It happens that renamevars() is one of the exceptions to this rule.

https://www.mathworks.com/help/matlab/ref/table.renamevars.html

I've attached a modified version of when() which should have fixes for issues 1 and 2. The latter issue just requires foreknowledge of how the URL is structured.

when table.renamevars
## [table.renamevars] does not exist (Introduced in R2020a).

Note that even though renamevars() exists in R2021a, the mismatch between the URL and function name causes when() to confusingly say it doesn't exist.

when renamevars
Connection error or no online documentation found for [renamevars].

If you use the expected filename, it acknowledges that it exists, but then it can't find the webdocs.

The impression now is probably that this is a huge waste of time, and that's a bit unfair. You just happened to have asked about something that's an exception to the rules. For most things, this modified version of when() should at least suffice to get a version. If you're stuck on a slow connection, or if you don't have enough system resources to squander rendering needlessly heavy web pages, when() is much faster than trying to look up web docs.

EDIT: read my comment below about a more robust version of when().

Walter Roberson 2021-8-10

在 MATLAB Online 中打开

renamevars() is a method of a class, rather than a function itself. Guessing the formal documentation URL for methods of a class can be tricky even assuming you know what class is being used. But the MATLAB class resolution algorithm is not as simple as "first parameter determines the class to look at", so even if you made this when() operate similar to which() in the ability to pass in the text of a calling expression, it would be easy to get the type wrong...

Some methods do not have separate documentation, and are only documented in the class description.

Some methods do not have separate documentation just for the method and are not documented in the main class description either, and you have to look on other pages...

... and why is the documentation page table.renamevars and not tabular.renamevars ?

which -all renamevars
/MATLAB/toolbox/matlab/datatypes/tabular/@tabular/renamevars.m  % tabular method
/MATLAB/toolbox/matlab/bigdata/@tall/renamevars.m               % Shadowed tall method
/MATLAB/toolbox/parallel/parallel/@distributed/renamevars.m     % Shadowed distributed method
/MATLAB/toolbox/parallel/parallel/@codistributed/renamevars.m   % Shadowed codistributed method

Then there is the problem that it is not uncommon for methods to not be known to MATLAB, not available for being found using which, until the class has been invoked (so that MATLAB brings the classdef and related routines into memory.)

Walter Roberson 2021-8-10

I have access to ISOs, and those contain all toolboxes. I do not, however, have licenses for all the toolboxes, so I cannot install everything (I think.)

It is possible to parse the manifests to find all the file names, but I have not figured out how the names of the manifest files relate to product names.

And just knowing the file names is not enough, since methods can be completely enclosed within their classes. And I have never found the way to figure out the complete list of built-in functions.

So, as users we can do more than "nothing" to create an appropriate database, but I'm not sure if we could get it right.

DGM 2021-8-11

编辑：DGM 2021-8-11

If one had a comprehensive set of the installation material, that might at least have the potential to be significantly more complete than other approaches. I mean, squeezing harder won't get legacy or toolbox-related information out of release notes if it's simply not there.

As far as I can see, the available options are all significant challenges in terms of effort and time, and they all lead to a result that is not only likely incomplete to an unknowable degree, but thereafter requires biannual maintenance as well. As I think Star Strider mentioned, you may also have to (programmatically) identify and deal with cases where functions changed name or moved from their original toolbox to the base toolbox. Whether that degree of rigor is warranted for an incomplete database probably depends on how incomplete it's assumed to be.

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