In R2014b there is currently not a direct way of creating a MAT file datastore. However, there are several indirect ways that will create a mat file datastore in R2014b.
The first method is to use the output of a mapreduce operation. That is, create an input file 'input.txt' that has the following contents:
Filename
myMatFile.mat
mySecondMatFile.mat
Then create a 'myMapper.m' with the following contents:
function myMapper(data, ~, intermediateOutput)
filenames = data.Filename;
addmulti(intermediateOutput, filenames, filenames);
end
And a 'myReducer.m' with the following contents:
function myReducer(filename, ~, finalOutput)
% This should be changed depending on the inputData.
% This purely converts a struct array into a cell array of structs for addmulti.
data = load(filename);
values = num2cell(data.myStructArrayVariable);
keys = repmat({'SomeKey'}, size(values));
addmulti(finalOutput, keys, values);
end
With all of this in place, do:
ds = datastore('input.txt');
mapFunction = @myMapper;
reduceFunction = @myReducer;
outputFolder = '/my/output/folder';
resultDS = mapreduce(ds, mapFunction, reduceFunction, 'OutputFolder', outputFolder)
This will create a collection of MAT files in the given output folder that consists of the original data and that can be used with datastore.
The second method is an unofficial shortcut to this. That is to do the following:-
% Suppose keys and values are two arrays of the same size such as:-
keys = {'TestKey1'; 'TestKey2'};
values = struct('Foo', {1,2}, 'Bar', {3,4});
% Then this will store data in such a way that it can likely be read by datastore:-
if ~iscell(keys)
keys = num2cell(keys);
end
if ~iscell(values)
values= num2cell(values);
end
data.Key = keys(:);
data.Value = values(:);
save('myMatFile.mat', '-struct', 'data');
ds = datastore('myMatFile.mat');
readall(ds)
