%PRDATAFILE Datafile class constructor. This is an extension of PRDATASET.
%
% A = PRDATAFILE(DIRECTORY,TYPE,READCMD,P1,P2,P3, ...)
% A = PRDATAFILE(DIRECTORY,READCMD,P1,P2,P3, ...)
%
% INPUT
% DIRECTORY - Data directory
% TYPE - Datafile type (default 'raw')
% READCMD - Command (m-file) for reading files in DIRECTORY.
% Default: IMREAD
% P1,P2,P3 - Optional parameters of READCMD
%
% OUTPUT
% A - Datafile
%
% DESCRIPTION
% Datafiles prepare and enable the handling of datasets distributed over
% multiple files, i.e. all files of DIRECTORY. Datafiles inherit all
% dataset fields. Consequently, most commands defined on datasets also
% operate on datafiles with the exception of a number of trainable
% mappings. There are five types of datafiles defined (TYPE):
% 'raw' Every file is interpreted as a single object in the
% dataset. All objects in the same sub-directory of
% DIRECTORY receive the name of that sub-directory as class
% label. Files may be preprocessed before conversion to
% dataset by FILTM. At conversion time they should have the
% same size (number of features).
% 'cell' All files in DIRECTORY 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' It is expected that READCMD outputs for all files a
% dataset with the same label list and the same feature size.
% 'half-baked' All files in DIRECTORY should be mat-files,
% containing a single dataset. All datasets should have the
% same label list and the same feature size.
% 'mature' This is a datafile directory constructed by SAVEDATAFILE.
% It executes all processing before creation.
%
%
% For all datafile types holds that execution of mappings (by FILTM or
% otherwise and conversion to a dataset (by DATASET) is postponed as long as
% possible. Commands are stored inside one of the datafile fields.
% Consequently, errors might be detected at a later stage.
%
% The construction by DATAFILE still might be time consuming as for some types
% all files have to be checked. For that reason PRTools attempts to save a
% mat-file with the DATAFILE definition in DIRECTORY. If it is encountered, it
% is loaded avoiding a redefinition.
%
% SEE ALSO (<a href="http://37steps.com/prtools">PRTools Guide</a>)
% DATAFILES, DATASETS, MAPPINGS, FILTM, SAVEDATAFILE, CREATEDATAFILE