Matlab struct with names and sizes of the mat.file

Hi, I am trying to create a function that asks for mat.file and then I would like t o create a struct which returns the name and size of the variables in the mat.file.

Anyone who knows how to do that?

Answer 1

[Walter Roberson]

Use whos() with the '-file' option and extract the required data from that.

[Robert Bag]

Thank you very much. But I am looking for a function that asks for a certain mat.file; loads the specific variables in the fields name and size and then puts them in a struct.

Kind of like prompt or so.

[Walter Roberson]

function info = fileinfo(filename)
   if ~exist(filename, 'file')
       info = [];
   else
       tinfo = whos('-file', filename);
       info = struct('name', {tinfo.name}, 'size', {tinfo.bytes});
   end
end

[Robert Bag]

Thanks a lot! But this just gives me the structure array. I want to get the variable sizes and their names in the structure array

[Walter Roberson]

But I am looking for a function that asks for a certain mat.file; loads the specific variables in the fields name and size and then puts them in a struct.

How do you want it to do the asking for the file? input()? uigetfile() ? menu() ?

What specific variables should be loaded?

Where is the field named name coming from?

If you have a field named name then how would the size come in? For example is the idea that you only load the content of the variable with the given name provided that its size matches the size given (somehow) ?

What is being put into a struct? Information about variable names and sizes? Contents of the variables?

I want to get the variable sizes and their names in the structure array

Is the idea that the user is passing in a struct that has fields name and sizes and the function is intended to load those specific variables out of the file and return a struct of them?

Is the idea that inside the given file there is a variable which is a struct, and you want to get information about the fields and the size of the fields, without loading the content of the variable? If so is the name of the variable known ahead of time, or does the function need to look through all of the variables stored in the file and find the one that is a struct?

[Robert Bag]

I would like an input().

Name of variables in the mat.file and their sizes-

I would like to have two fields; name and size.

In short, I am looking for a kind of "whos" function without using whos.

Lets say i have saved a workspace in a mat.file. I have 8 variebles. I want a function in which I can input a name of the mat.file through a prompt, and which then extracts the fields: name and size of all the 8 variables in a list - just as what you get when you run whos with just two fields names and sizes. I would like the function to return a structure array.

like this but as function:

> whos ('-file', 'workspace313.mat')

Name Size Bytes Class Attributes

R 60x30 14400 double

ph 60x30 14400 double

phi 1x60 480 double

th 60x30 14400 double

theta 1x30 240 double

x 60x30 14400 double

y 60x30 14400 double

z 60x30 14400 double

[Walter Roberson]

Everything except the input() is what the function I posted already does. It processes the given file name and returns a struct array with fields named name and size

... oh wait, you wanted the other meaning of size:

function info = fileinfo(filename)
   if ~exist(filename, 'file')
       info = [];
   else
       tinfo = whos('-file', filename);
       info = struct('name', {tinfo.name}, 'size', {tinfo.size});
   end
end

[Robert Bag]

Yes. Please

[Robert Bag]

I just got this:

fileinfo('workspace313.mat')

ans =

1×8 struct array with fields:

name

size

[Walter Roberson]

That looks to be a correct result based on what you told us before.

info = fileinfo('workspace313.mat')
info(1).name
info(1).size

Were you instead looking for a scalar struct in which the field name was a cell array of character vectors listing the variable names, and the field size was a cell array of corresponding sizes?

info =

  struct with fields:
  name: {'a'  'b'  'cafd'  'afdafdfa'  'adfa'  'afag'}
  size: {[3 8]  [17 9 3]  [512 2018] (and so on)}

If so that is certainly possible. You would get out the information using, for example,

  info.name{1}
  info.size{1}

[Robert Bag]

Walter, is there any way to get whos to obly display specific fields?

[Walter Roberson]

whos() is built-in, so I cannot look at the source code for it. There is no documented way to get whos() to only display specified fields.

But why are you asking about displaying fields? Your question and comments indicate that you want the information returned as a struct with field 'name' and 'size' . Displaying is a different task.

The below code has been constructed to mimic the output of whos. It might have some fine details wrong about automatic sizing or justification of field widths.

function info = fileinfo(filename)
   if ~exist(filename, 'file')
       error(message('MATLAB:whos:fileIsNotThere', filename));
   end
   tinfo = whos('-file', filename);
   if nargout > 0
       info = struct('name', {tinfo.name}, 'size', {tinfo.size});
   else
       fields = ["name", "size"; "", ""; string({tinfo.name}.'), cellfun(@(S) strjoin(arrayfun(@string,S),'x'), {tinfo.size}.')];
       L = strlength(fields);
       widths = max(L,[],1);
       fmt = compose("  %%-%ds %%-%ds", max([14, 0], widths));
       fprintf('%s\n', compose(fmt, fields(:,1), fields(:,2)))
   end
end