How to load in variable if it is present in a matfile?

Question

K E 2015-7-21

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/230682-how-to-load-in-variable-if-it-is-present-in-a-matfile

评论： K E 2015-7-24

I am having trouble with "conditional" loading of a variable from a matfile, depending on whether the matfile contains the variable. Here is what I am trying to do:

Go through many different (large) matfiles, some of which contain mountain height in a variable called topo, and some of which contain mountain height in variable called elevation.
If the matfile contains the variable topo, load that into a workspace variable called mountainHeight. If the matfile contains the variable elevation, load that into a workspace variable called mountainHeight. If neither variable is contained in matfile, do nothing.
Avoid crashing the load command by trying to load variables which are not in the matfile.

Here is what I have tried (R2015a), but I'd bet there is a better/shorter way.

filename = 'topography.mat'; % A matfile that comes with matlab
m = matfile(filename); % Make a matfile object
FileInfo = whos(m); % Structure containing information about matfile including variables it contains
for iVar = 1:length(FileInfo)
    if strcmp(FileInfo(iVar).name, 'topo') % Check if topo is a variable in topography.mat
        mountainHeight = m.topo; % Load topo 
    elseif strcmp(FileInfo(iVar).name, 'elevation') % Check if elevation is a variable in topography.mat
        mountainHeight = m.elevation; % Load elevation
    end
end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Steven Lord 2015-7-21

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/230682-how-to-load-in-variable-if-it-is-present-in-a-matfile#answer_186799

在 MATLAB Online 中打开

 D = load('mymatfile.mat');
 if isfield(D, 'elevation')
  elevation = D.elevation;
 else
  elevation = NaN;
 end

Alternately, check if the field exists and if it doesn't, add it with some placeholder data.

 D = load('mymatfile.mat');
 if ~isfield(D, 'elevation')
  D.elevation = NaN;
 end

If you want to do this with multiple fields, use dynamic field names.

 D = load('mymatfile.mat');
 listOfFields = {'elevation', 'material', 'price'};
 isPresent = isfield(D, listOfFields);
 for fieldnum = 1:length(listOfFields)
   if ~isPresent(fieldnum)
     F = listOfFields{fieldnum};
     D.(F) = NaN;
   end
 end

7 个评论
显示 5更早的评论隐藏 5更早的评论

K E 2015-7-23

Cedric - These matfiles are generated by many different authors and I want to keep track of the originals so I am stuck making my code accommodate the inconsistent names.

Cedric 2015-7-23

编辑：Cedric 2015-7-23

在 MATLAB Online 中打开

Then just build a small function that does what Steven proposes, and outputs mountainHeight:

 function mountainHeight = loadMountainHeight( locator )
    data = load( locator ) ;
    if isfield( data, 'topo' )
       mountainHeight = data.topo ;
    elseif isfield( data, 'elevation' )
       mountainHeight = data.elevation ; 
    else
       mountainHeight = [] ; % Or NaN or whatever you want, to tell
                             % the caller "field not found".
    end
 end

Then in your main script, you do something like the following:

 dir_mat = dir( '*.mat' ) ;
 for fId = 1 : numel( dir_mat )
    mountainHeight = loadMountainHeight( dir_mat(fId).name ) ;
    if isempty( mountainHeight )
       % Throw warning, or print message, or just skip.
       warning( 'File "%s" : no valid field found!', dir_mat(fId).name ) ;
       continue ;
    end
    fprintf( 'File "%s" : processing height..\n', dir_mat(fId).name ) ;
    % .. code for further processing mountainHeight ..
 end