MATLAB Changing the name of a matrix with each iteration

Question

I was just wondering if there is a clean way to store a matrix after each iteration with a different name? I would like to be able to store each matrix (uMatrix) under a dif

Answer 1

There are really too many options. To go describe both putting data into, and getting data our of a few of these methods:

Encode in variable names

I really, really dislike this approach, but it seems to be what you are specifically asking for. To save uMatrix as a variable Sim5 (after the 5th run), add the following to your code at the end of the loop:

eval([Sim ' = uMatrix;']);  %Where the variable "Sim" contains a string like 'Sim5'

To access the data

listOfStoredDataNames = who('Sim*')
someStoredDataItem = eval(listOfStoredDataNames {1})  %Ugghh
%or of you know the name already
someStoredDataItem = Sim1;

Now, please don't do this. Let me try and convince you that there are better ways.

Use a structure

To do the same thing, using a structure called (for example) simResults

simResults.(Sim) = uMatrix;

or even better

simResults.(genvarname(Sim)) = uMatrix;

To access the data

listOfStoredDataNames = fieldnames(simResults)
someStoredDataItem = simResults.(listOfStoredDataNames{1})
%or of you know the name already
someStoredDataItem = simResults.Sim1

This avoids the always problematic eval statement, and more importantly makes additional code much easier to write. For example you can easily pass all simResults into a function for further processing.

Use a Map

To use a map to do the same storage, first initialize the map

simResults = containers.Map('keyType','char','valueType','any');

Then at each iteration add the values to the map

simResults(Sim) = uMatrix;

To access the data

listOfStoredDataNames = simResults.keys
someStoredDataItem = simResults(listOfStoredDataNames{1})
%or of you know the name already
someStoredDataItem = simResults('Sim1')

Maps are a little more flexible in the strings which can be used for names, and are probably a better solution if you are comfortable.

Use a cell array

For simple, no nonsense storage of the results

simResults{i} = uMatrix;

To access the data

listOfStoredDataNames = {};  %Names are Not available using this method
someStoredDataItem = simResults{1}

Or, using a slight level of nonesense

simResults{i,1} = Sim;      %Store the name in column 1
simResults{i,2} = uMatrix;  %Store the result in column 2

To access the data

listOfStoredDataNames = simResults(:,1)
someStoredDataItem = simResults{1,2}

Answer 2

I would try to use a map which stores a <name, matrix>. the possible way to do it would be to use http://www.mathworks.com/help/matlab/map-containers.html

Answer 3

Just to add to the detailed answer given by @Pursuit, there is one further method I am fond of:

Use an array of structures

Each item in the array is a structure which stores the results and any additional information:

simResults(i).name = Sim;         % store the name of the run
simResults(i).uMatrix = uMatrix;  % store the results 
simResults(i).time = toc;         % store the time taken to do this run

etc. Each element in the array will need to have the same fields. You can use quick operations to extract all the elements from the array, for example to see the timings of each run at a glance you can do:

[simResults.time]

You can also use arrayfun to to a process on each element in the array:

anon_evaluation_func = @(x)( evaluate_uMatrix( x.uMatrix ) );
results = arrayfun( anon_evaluation_func, simResults );

or in a more simple syntax,

for i = 1:length(simResults)
    simResults(i).result = evaluate_uMatrix( simResults(i).uMatrix );
end