Structure indexing: Convert cell to string without trailing spaces

Hi all,

I am looking for some help on how one converts cells to string arrays without all the trailing space. I am sure I am making things too complex. What I am doing in short, is setting up a function that returns spectral indices based on literature-published indices. The basic information for each index will be stored in a structure, which eventually I might make a separate file.

If a user wants all the indices, rather than asking them to provide all the indices by name, I will allow a key word 'all'. At that point, I take the fieldnames of the structure to give me the fieldnames to use. This is where things go wrong, as the fieldnames are in cells. I have tried

indice_names  = fieldnames(indices_specs);
indice_names  = char(indice_names);

But then all the strings have trailing spaces. I can probably trim those again, but.. Is there a more straightforward way to go about this?

To give you some insight, this is what I am working on debugging (And no, none of the function calls to JF_calculate_vegetation_index work yet. The function itself does not even have content yet):

function out_indices = jf_calculate_vegetation_indices(spectra, offset, indice_names)
  % Matlab:       2015b
  % Purpose 
  % Calculate well-known hyperspectral indices vegatation indices 
  % 
  % Parameters
  % "Spectra"      Input spectra in in an array, colums individual spectra, rows: samples
  % "offset"      The first wavelength of the spectrum. 1nm spacings are expected
  % "indices"       The name of the indices to be calculated in an array. 
                    %Use a string "all" for all indices to be returned. 

    %%get all set up 
    num_indices        = max(size(indice_names));
    [num_samples,num_bands]  = size(spectra);
    wavelengths       = [offset:offset+num_bands];

    %%create an structure that specifies all the info needed for each index in the setup
    indices_specs.GI     = struct('type', 'ri', 'bands',   [554,677], ...
      'name', 'GI',       'fullname', 'Green index', 'author', 'smith', 'year', '1995');
    indices_specs.ZTM     = struct('type', 'ri', 'bands',   [750, 710], ...
    'name', 'ZTM',      'fullname', 'Zarco-Tejada & Miller', 'author', 'Zarco-Tejeda', 'year', '2001');
    indices_specs.PSSRa   = struct('type', 'ri', 'bands',   [800,806],   ...
    'name', 'PSSRa',  'fullname', 'Pigment specific simple ratio a', 'author', 'blackburn', 'year', '1998');
    indices_specs.PSSRb   = struct('type', 'ri', 'bands',   [800,635], ...
      'name', 'PSSRb',  'fullname', 'Pigment specific simple ratio b', 'author', 'blackburn', 'year', '1998');

    % Check whether the key word "all" was set for the indices. Then create a
    % list of name labels from the structure

    if(indice_names == 'all')
      indice_names  = fieldnames(indices_specs)'
      num_indices   = max(size(indice_names));
    end

   %%run the indices_specs
      for i=1:num_indices

        if(indices_specs.(indice_names(i)).type == 'other')
        
          out_indices.(indice_names(i)).name = indice_names(i);
          out_indices.(indice_names(i)).data = JF_calculate_vegetation_index(indices_specs.(indice_names(i)).type, spectra, indices_specs.(indice_names(i)).name);
      
      else

          out_indices.(indice_names(i)).name = indice_names(i);
          out_indices.(indice_names(i)).data = JF_calculate_vegetation_index(indices_specs.(indice_names(i)).type, spectra(:,indices_specs.(indice_names(i)).bands));

      end
      
      end

    end

Answer 1

[Walter Roberson]

    if strcmp(indice_names, 'all')
      indice_names  = fieldnames(indices_specs);
    else
      indice_names = cellstr(indice_names);
    end

    num_indices   = length(indice_names);

   %%run the indices_specs
      for i=1:num_indices

        thisname = incides_names{i};
        if strcmp(indices_specs.(thisname).type, 'other')
        
          out_indices.(thisname).name = thisname;
          out_indices.(thisname).data = JF_calculate_vegetation_index(indices_specs.(thisname).type, spectra, indices_specs.(thisname).name);
      
      else

          out_indices.(thisname).name = thisname;
          out_indices.(thisname).data = JF_calculate_vegetation_index(indices_specs.(thisname).type, spectra(:,indices_specs.(thisname).bands));

      end
      
      end

Answer 2

[Jelle]

Cool, thanks. Not exactly the code I was looking for but it helped me in the direction.

It now looks like this:

if(indice_names == 'all') % change to strcmp
  indice_names  = fieldnames(indices_specs);
  num_indices   = max(size(indice_names));
end

%%run the indices_specs
  for i=1:num_indices

      thisindex = indice_names{i};

    % adjust the wavelengths for the offset in the inspectra
      usedbands = indices_specs.(thisindex).wavelengths - (offset-1);

      out_indices.(thisindex).name = thisindex;
      out_indices.(thisindex).data = JF_calculate_vegetation_index(indices_specs.(thisindex).type, indices_specs.(thisindex).name, spectra(:,usedbands));

    end

end

[Walter Roberson]

indice_names == 'all' is wrong unless the user is passing in string objects (created with double quotes) instead of character vectors (created with single quotes.)

Using indice_names{i} is wrong if the user did not pass in 'all', unless they happened to pass in a cell array of character vectors or a string array. If they passed in a single character vector other than 'all' then it will not be a cell array. The adjustment for that is cellstr(), which will convert a character vector to a 1 x 1 cell array containing the character vector but will leave an existing cell array of character vectors alone.

[Jelle]

Hi Walter,

Thank you for your continued help!

I noticed the comparison operator too as I was posting the answer. As I was on my way home I just added the comment in there that I will have to make that strcmp.

Good point with the indice_names{i}. I did not realize that. (I am just learning the language, obviously..). Will adjust the code to what you suggested and not try to be too clever for my own good. Sorry!

I will do a bit of testing on my side with the code I have now. I am sure this will make it clear what exactly goes wrong with my version, helping me better understand the differences. A bit hard to get my head around all the different types of dataformats in matlab. And the manual is really only of good help for me once I know matlab and the data types better. So your help is highly appreciated!