MATLAB Answers

Error trying to load a file in MATLAB Grader

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William Stuckey
William Stuckey on 28 Jan 2020
Commented: William Stuckey on 31 Jan 2020
I'm trying to load an Excel file (one column of numbers) in a MATLAB Grader script and getting an "Error using load" that says, "Number of columns on line 2 of ASCII file NavyData.xlsx must be the same as previous lines." I have no idea how to fix that error, because I don't know what it even means. Any suggestions?


Geoff Hayes
Geoff Hayes on 28 Jan 2020
William - can you use load with an Excel file (see load filename input parameter)? Why not convert the Excel file into an ASCII text file and try that instead?

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Answers (1)

Cris LaPierre
Cris LaPierre on 30 Jan 2020
It depends on what the end task is you are trying to achieve, but my recommendation would be to use readtable.


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William Stuckey
William Stuckey on 30 Jan 2020
Thnx, I did the Teaching with MATLAB course and I'm creating assignments in MATLAB Grader for my students now (that's where this issue arose). I'm gradually learning more of MATLAB's capabilities as I teach the course (this is my third time through with MATLAB). I'm an old physicist and the computer terminology is very different today than when I was a student (1980-87), so some of the terminology used in online explanations is Greek to me :-)
Cris LaPierre
Cris LaPierre on 31 Jan 2020
One thing that might help is the example problems that come with MATLAB Grader.
When you create a new problem, you are presented with what we call the problem chooser. There, you will see several tiles. Under the "Sample Problems from MathWorks" is a tile called "Getting Started with MATLAB Grader" (there are several others organized by topics such as Intro to Programming, Numerical Methods, Dynamics, System Dynamics and Controls, etc. If you don't see them but would like access, contact customer support to submit a request. They are free but access is restricted to instructors).
As the title suggests, these problems demonstrate how to accomplish various tasks. The best way to see what problem does what is to look at the table at the very end of the Teaching with MATLAB course. I'd point out these two problems in particular.
  • Analysis of stress-strain data. This uses readtable to load a *.xlsx file into the workspace.
  • Determine the drag coefficient by fitting a polynomial to velocity-force data. This uses readtable to load a *.csv file into the workspace.
Hopefully these help you. There are extra comments added to some of the assessment tests to explain what is being done.

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