Loading data from .mat file and converting them to string array

I need to create a .mat file in which I save a string array using the following two command lines (the original array could be much larger):

Grades={'CB 21'; 'CB 22'; 'CB 24'; 'CB 25'};
save GradNames.mat Grades

but when I try to read the data from it and asign them to the array GN by:

load ('GradNames.mat', 'GN')

MATLAB returns the warning:

Warning: Variable 'GN' not found.

In Save2Mat (line 5)

Answer 1

[Les Beckham]

You only save one variable into the mat file and its name is Grades.

The syntax load('matfilename.mat', 'varname') tries to find a variable named varname in the matfile. Since your mat file doesn't contain a variable called GN, you get the error.

If you do load('GradNames.mat') you will see that your variable Grades will appear in the workspace and you can copy it to GN if you want to.

However, it is generally recommended to load mat files into a data structure so you won't accidentally overwrite an existing variable in your workspace (especially if you aren't sure what is inside the mat file.

To do this, use syntax like this: GN = load('GradNames.mat'). For example:

Grades={'CB 21'; 'CB 22'; 'CB 24'; 'CB 25'};
save('GradNames.mat', 'Grades');
clearvars % clear the workspace
GN = load('GradNames.mat');
whos % check what is in the workspace

  Name      Size            Bytes  Class     Attributes

  GN        1x1               624  struct              

GN

GN = struct with fields:
    Grades: {4×1 cell}

GN.Grades % now the original Grades cell array is a member of the GN struct

ans = 4×1 cell array
    {'CB 21'}
    {'CB 22'}
    {'CB 24'}
    {'CB 25'}

[Saeid]

Thank you, Les.

[Les Beckham]

You are quite welcome. Glad I could help.

Answer 2

[Walter Roberson]

load ('GradNames.mat', 'GN')

means that a variable named GN is to be looked for inside the file, and if it is found, loaded into the workspace. It does not take whatever variable is found in the file and assign it to GN . (Imagine the problems that syntax would have if there were more than one variable in the file.)

datastruct = load('GradNames.mat', 'Grades');
GN = datastruct.Grades;

[Saeid]

Thanks, Walter!