Datafile definition

Datafile definition

Constructor

The datafile constructor looks like

    a = datafile(directory,type,readcommand,par1,par2,... )

• directory is the name of the directory on disk where the data is stored.
• type is the type of datafile, see below. It may be omitted for the default, standard, raw datafile.
• readcommand is a string with the name of the command used to read individual files (objects). Default is imread.
• par1, par2, are additional parameters needed for readcommand.

Datafile types

There are five types supported for datafiles:

• raw: Every file is interpreted as a single object in the dataset. Files should be organized in directories of objects that belong to the same class. Directory names will be the class names. Files in the main directories are interpreted as unlabeled objects. Files may, for instance, be images of different size. This is the standard, default type.
• cell: All files should be mat-files containing just a single variable being a cell array. Its elements are interpreted as objects. The file names will be used as labels during construction. This may be changed by the user afterwards.
• pre-cooked: In this case readcommand should be a user defined command that converts individual files into a dataset.
• half-baked: All files should be mat-files, containing a single dataset.
• mature: This is a datafile as constructed by PRTools, using the savedatafile command after execution of all preprocessing defined for the datafile.

The raw type is the original, standard type. It is useful for raw date like images, time signals and spectra. The user should organize the files class-wise in sub-directories before the datafile constructor is called.

An important point to note is that in the datafile constructor call a mat-file with all information is stored in directory. This is done to speed up loading of an existing, earlier defined datafile, as the constructor may be time consuming because all directories, and for some types, all files have to be inspected.

Datafile structure

The below information is only important for maintenance and not for users.

Datafiles are children of the programming class dataset. It adds a few fields. These can be found by converting a datafile variable into a structure. In the following example the ORL face database is used. If it is not available, it will be downloaded from the PRTools website as a datafile.

    a = orl;
%       ORL faces, raw datafile with 400 objects in 40 crisp classes: [10  10  10  10 ...
    struct(a)
%
%       files: {{1x41 cell}  {1x41 cell}}
%    rootpath: 'D:\bduin\Desktop\prdatafiles\orl'
%        type: 'raw'
%     preproc: [1x1 struct]
%    postproc: [0x0 mapping]
%     dataset: [400x10304 dataset]

Most fields have set- and get- routines (e.g. setfiles and getfiles) to define or retrieve their values. Users are discouraged to use the '.'-constructs (e.g. a.files) as it will not guarantee consistency with other fields. In the table more information on the fields is given.

Datafile definition