how do I get the value of a variable from the base workspace in my GUI??

Hi,

i have a large workspace (±400 variables) and i want to write a script for my gui, where i can put in a variable in an edit box, press a button next to it, and then the value of this variable has to appear in an other edit box. I'm really stuck on this, does anybody know how to do this???

Greetings

[Azzi Abdelmalek]

how many edit box

[Edward]

one edit box to for the name of a variable, and one edit box where the value corresponding to this variable appears. Also there is a button, which has to run the script that gets de data from the workspace an shows it in the second edit box.

Answer 1

[Milos]

You can use this:

varName = evalin('base', 'varNameInWorkspace');

[Edward]

okay, but 'varNameInWorkspace' has to be editable from within the GUI. So therefore, in the Callback function of the first edit box, a variable 'varNameInWorkspace', i guess? Something like:

get(hObject,'String',handles.varNameInWorkspace)

?

[Milos]

Let's say the tags are box1, box2, button1. User enters the desired variable name in box1, the name in the Workspace is var1Name. In push button function, place the following code:

vn1 = get(handles.box1, 'String');
vv1 = evalin('base', vn1);
numRow = size(vv1, 1);
set(handles.box2, 'Max', numRow);
set(handles.box2, 'String', num2str(vv1));

[Edward]

thanks!

[m naveed]

@Milos you are awesome man. solved my problem which i was stuck in for so many days

[Stephen23]

Note that using evalin is the least recommended method of passing data between workspaces:

https://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

No matter how much some beginners love telling each other to use this method, it is slow and buggy. The MATLAB documentation explains the preferred ways of passing data between workspaces:

http://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

And read this to know why eval and evalin should be avoided:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

[Plinio Andrade]

Stephen,

Please stop calling other people begginers. It sounds quite arrogant. Also, stop pointing people to other forum discussion with an valid ansewer given by yourself.

Sincerely,

[Stephen23]

@Plinio Andrade: thank you for your comments, I appreciate the feedback.

"Please stop calling other people begginers. It sounds quite arrogant."

I have observed, over more than fifteen years of reading this and other forums, that use of dynamically named variables is highly correlated with beginners learning how to write code. It seems that there is something intuitive that some beginners** find about the idea of changing variable names, whilst they might simultaneously struggle with basic coding concepts (such as indexing into an output variable in a loop). This is simply an observation, based on countless threads on this and other forums.

It is not clear to me if it is also "arrogant" to state the fact that some beginners** struggle to understand indexing, or struggle to understand code vectorization: do these statements of fact also seem "arrogant" to you? It is not my intention to be arrogant, but to get the attention of those learners who are pointlessly forcing themselves into writing complex code, and to show them that there are much better alternatives, (which are simpler, more reliable, and much more efficient). I do not use the word "beginner" as a perjorative, simply as a factual description to get their attention. Would "new users" be better? Would "some users" get the same attention?

** not all, but certainly at a higher rate than more experienced users.

"Also, stop pointing people to other forum discussion with an valid ansewer given by yourself."

Posting links to valid answers is perfectly acceptable on this forum, this is regularly used by most regular contributors that I can think of. It certainly saves a lot of effort when an existing valid answer already covers some topic in detail. What do you propose instead?

You have make your criticism clear, and I appreciate that. Now based on your negative criticisms you can help me as well with some constructive answers to my two questions:

1. How should I phrase a concise comment to really get the attention of someone who is (most likely) new to writing code and is approaching something in the wrong way? What should I write that really gets their attention and makes it clear that their approach is counter-productive?
2. What do you propose instead of posting links to existing valid answers? Should I copy the entire text of the thread (including all answers and comments)?

I look forward to reading your constructive help and answers to my two questions.

Regards,

Stephen

[Vadim Kachan]

Shots fired^

[Mohammad Shokrian Amiri]

@Stephen the reason some people ask a question - that is in your mind counter-productive and bad coding habit - might NOT be that they are beginners or do not know what they are doing!! I am here looking for answers because I am struggling with a PROBLEM! and instead I find answers that mostly say "it's simple, do not do it"

I cannot speak for everyone but in my case for example, I am dealing with an old workspace load that is a year worth of measurement data done by someone else, and I am trying to go through it. But in order to do so in a shorter time, I need to write a code to sort them out instead of manually dig into it! so I am loading the data but I need a way to make matlab read my workspace, take the variable name, and put it in another, as you prefer it, array!

[Rik]

Sound like you need to load to a struct. That way you can use the fieldnames function to loop through all variables to store them in the appropriate array.

So again, no need for eval. That is the point. You should not assume eval is the answer. I haven't really seen a situation where there wasn't a solution. Well, one only: defining an anonymous function in an m file will cause a syntax error in Matlab 6.5, because that isn't a valid syntax. And maybe there is a workaround even there.

If you have a problem, explain the problem. The issue is that many people end the explanation of their problem with 'how can I use eval to do this'.

[Stephen23]

@Mohammad Shokrian Amiri: It is curious that you think "that is in your mind counter-productive and bad coding habit": the fact that this approach leads to slow, complex, inefficient code that is harder to debug is objective reality that has nothing to do with my poor little mind. The fact that the MATLAB documentation states here "Best Practice: Passing Arguments" and places evaluating variables in another workspace at the end of the list... also has nothing to do with my mind. You can confirm those facts yourself.

I completely agree that simply writing "do not do it" is not very useful. That is exactly why:

• I started this thread which contains explanations/links of the main disadvantages and also explanations/links to the better (faster, neater, simpler, more robust) alternatives. So any user who actually wants to learn has the opportunity to do so.
• on many threads where the OP/commenter has given sufficient information I also write a comment/answer that shows a more efficient and more robust approach, with code and links to help them. Feel free to read my many comments and answers on this topic to confirm that yourself.

"...I am struggling with a PROBLEM!"

You will also find several threads on this forum discussing the meta-topic of whether the active users on this forum should only answer the exact question that the OP asked (even if this leads to them wasting significant amounts of their own time and writing pointlessly complex and inefficient code) vs. giving advice based on our combined thousands-of-hours and millions-of-lines of experience. Which would you prefer? And if the latter, how should it be phrased to effectively communicate its content?

As Rik already commented, most likely your code would be improved by LOADing into an output variable.