# Trying to randomly permute a time series, error with time point

3 Ansichten (letzte 30 Tage)
Joanne Hall am 2 Mai 2023
Bearbeitet: Joanne Hall am 3 Mai 2023
Dear Matlab,
I have an EEG signal, which I ran through wavelet convolution to produce a 3D matrix of time-frequency values, that is:
1 X 68(frex) X 4000(time points)
GOAL: Now the next step is to randomly slice the tf matrix and reoder time zero (and effectively reorder the map, to 'shuffle' it), by running the tf map/variable through 1000 rounds of permutations.
(see code below here, and attached tf mat file to run it):
% PERMING power values
num_iterations = 1000;
permuted_results = zeros(num_iterations,length(frex),length(times2));%zeros(1,num_iterations);
for ni=1:num_iterations
% randomly resort power values
cutpoint = times2(randi(numel(times2)));
permuted_results(ni,:,:,:) = tf(:,:,[ cutpoint:end 1:cutpoint-1 ]);
end
PROBLEM: when I run the for loop, I get this error:
Index in position 3 is invalid. Array indices must be positive integers or logical values.
Is it because the time series, which goes from -1000 to 3000 milliseconds, is it the negative values in there?
Thanks very much in advance for any help/guidance!
Best,
Joanne
##### 2 KommentareKeine anzeigenKeine ausblenden
Dyuman Joshi am 2 Mai 2023
"Is it because the time series, which goes from -1000 to 3000 milliseconds, is it the negative values in there?"
Yes.
num_iterations = 1000;
permuted_results = zeros(num_iterations,length(frex),length(times2));%zeros(1,num_iterations);
for ni=1:num_iterations
% randomly resort power values
cutpoint = times2(randi(numel(times2)))
permuted_results(ni,:,:,:) = tf(:,:,[ cutpoint:end 1:cutpoint-1 ]);
end
cutpoint = 2956
cutpoint = 119
cutpoint = -130
Index in position 3 is invalid. Array indices must be positive integers or logical values.
Joanne Hall am 2 Mai 2023
How to fix?

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### Akzeptierte Antwort

A=[1 2 3 4 5 6 7]
A = 1×7
1 2 3 4 5 6 7
A(1:3)
ans = 1×3
1 2 3
A(-1:2)
Array indices must be positive integers or logical values.
Yes, Matlab needs the index of the position starting from 1, so if you use negative numbers there will be an error.
##### 6 Kommentare4 ältere Kommentare anzeigen4 ältere Kommentare ausblenden
Dyuman Joshi am 3 Mai 2023
"How to fix?"
It depends on what you want to do.
You can either use abs()
cutpoint = abs(times2(randi(numel(times2))))
or add 1001 to times2 (as suggested above) to adjust its values, which will change to 1 to 4001 (milliseconds).
times2 = times2 + 10001;
cutpoint = times(randi(numel(times2)))
%similar to the above two lines
cutpoint = randi(numel(times2))
Joanne Hall am 3 Mai 2023
Bearbeitet: Joanne Hall am 3 Mai 2023
Dyuman, I tried abs and it worked!! Thank you!!!
(and thank you also Constantino!)

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