Turn a structure into an array

Hello everybody,

i'm starting with matlab and i have a problem with this code:

ev = load('EV.mat'); %potenciales evocados
fs = 3200; %sampling rate = 3200 Hz
slen = length(ev);
t=[1:slen]/fs;
vent=256; %amplitud ventana
sum=zeros(1,vent); %vector de ceros con 256 elementos
n=100;   %numero de realizaciones

for i=0:vent-1
  for k=1:25600
      sum(i+1)=sum(i+1)+ev(i+k);
      k=k+256;
  end
end

i should sum 100 windows, each one containing 256 samples, of the same signal, the signal ev.Tthe problem is that the program gives me the following errors:

??? Undefined function or variable 'ev'.

??? Undefined function or method 'plus' for input arguments of type 'struct'.

Error in ==> Potenciales_Evocados at 17 sum(i+1)=sum(i+1)+ev(i+k);

Then, i guess i should transform this structure into an array, but i don't know how..! I've tried with "c = struct2cell(s)" but i create a cell array and the error is the same ??? Undefined function or method 'plus' for input arguments of type 'cell'.

In the command window i have this:

ev =

    ev: [727040x1 double]

>> length(ev)

ans =

     1
Please can anyone help me? Thank you very much in advance

Answer 1

[Jan]

It seems like after:

ev = load('EV.mat')

"ev" is a struct, which contains the field "ev". So try this:

Data = load('EV.mat')
ev   = Data.ev;

BTW. using "sum" as name of a variable shadows the built-in function with the same name. It is recommend to avoid such shadowing, because it leads to unexpected results frequently.

A faster method to sum the chunks without loops:

S = sum(reshape(ev, 256, []), 2);

[Sara]

Perfect!! Thanks a lot!!