Question

I have a loop which iterates for 97 times and there are two arrrays

1. frequency[1024]
2. strength[1024]

these arrays change values after each iteration of the loop. so before its value changes i need to put them in a structure.For instance the structure would be something like

s(1).frame=1        %this will show the iteration no.   
s(1).str=strength  
s(1).freq=frequency  

now i need 97 such structures say s(1) to s(97) in an array.

my question is: how can I create an array of structures within my loop. Please help me.

Answer 1

I like to iterate backward in cases like this, as this forces a full memory allocation the first time the loop is executed. Then the code would look something like this:

%Reset the structure
s = struct;
for ix = 97:-1:1
    %Do stuff

    %Store the data
    s(ix).frame = ix;
    s(ix).str = strength;
    s(ix).freq = frequency;
end

If one frame depends on the next, or you don’t know how many total frame there will be, you can scan forwards. 97 frames is not a lot of data, so you probably don;t need to worry too much about optimizing the pre-allocation portion of the problem.

%Reset the structure
s = struct;
for ix = 1:97
    %Do stuff

    %Store the data
    s(ix).frame = ix;
    s(ix).str = strength;
    s(ix).freq = frequency;
end

Or, if you really need to performance of a pre-allocated array of structures, but you don’t know how large it will be at the onset, you can do something like this:

%Reset the structure
s = struct;
for ix = 1:97
    %Do stuff

    %Extend if needed
    if length(s)<ix
        s(ix*2).frame = nan;  %Double allocation every time you reach the end.
    end

    %Store the data
    s(ix).frame = ix;
    s(ix).str = strength;
    s(ix).freq = frequency;
end

%Clip extra allocation
s = s(1:ix);