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

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Joanne Hall
Joanne Hall 2023-5-2
编辑： Joanne Hall 2023-5-3
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 个评论
Dyuman Joshi
Dyuman Joshi 2023-5-2
Ran in:
"Is it because the time series, which goes from -1000 to 3000 milliseconds, is it the negative values in there?"
Yes.
load('TFsample.mat')% 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
cutpoint = 2956
cutpoint = 119
cutpoint = -130
Index in position 3 is invalid. Array indices must be positive integers or logical values.

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采纳的回答

Constantino Carlos Reyes-Aldasoro
Ran in:
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 个评论
显示 4更早的评论
Dyuman Joshi
Dyuman Joshi 2023-5-3
"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
Joanne Hall 2023-5-3
编辑：Joanne Hall 2023-5-3
Dyuman, I tried abs and it worked!! Thank you!!!
(and thank you also Constantino!)

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