# Problems with indexing into an array with nan (indexing on 2 variables)

25 views (last 30 days)
PAK on 23 Aug 2018
Commented: PAK on 30 Aug 2018
Hi All,
I'm having trouble using a logical variable ( Bandphase_logical = 9x5272240 logical) to find "true" events in another variable ( bandphase = 3x5272240 single). I think part of my problem is that the "bandphase" variable contains NaNs and I am trying to index over 2 different variables (see below).
"Bandphase_logical" contains 1's where an event occurs across a time series (5272240 samples). "bandphase" contains radian values across the entire timeseries (5272240 samples). Each row contains different frequency bands, and has a "NaN" where that sample does that have a frequency.
I'd like to do something along the lines of (I'd to create a loop where the bandphase variable changes adaptively with how many rows it has and same with the Bandphase_logical variable [e.g.: if bandphase had 5 rows and Bandphase_logical had 12 rows]):
bandphase(1,:)(Bandphase_logical(1,:)
bandphase(1,:)(Bandphase_logical(2,:)
.
.
bandphase(1,:)(Bandphase_logical(9,:)
bandphase(2,:)(Bandphase_logical(1,:)
bandphase(2,:)(Bandphase_logical(2,:)
.
.
bandphase(2,:)(Bandphase_logical(9,:)
bandphase(3,:)(Bandphase_logical(1,:)
bandphase(3,:)(Bandphase_logical(2,:)
.
.
bandphase(3,:)(Bandphase_logical(9,:)
I'd greatly appreciate any help! I'm thoroughly confused.
PK

Stephen Cobeldick on 23 Aug 2018
Edited: Stephen Cobeldick on 23 Aug 2018
for ii = 1:size(bandphase,1)
for jj = 1:size(Bandphase_logical,1)
tmp = bandphase(ii,:);
tmp(Bandphase_logical(jj,:))
end
end
To store the output (of different sizes) use a cell array:
S = [size(bandphase,1),size(Bandphase_logical,1)];
C = cell(S);
for ii = 1:S(1)
for jj = 1:S(2)
tmp = bandphase(ii,:);
C{ii,jj} = tmp(Bandphase_logical(jj,:))
end
end

Stephen Cobeldick on 23 Aug 2018
Hi Stephen and Walter,
This does work! I created a variable to store "tmp(Bandphase_logical(jj,:)). However, how do I make that variable ("phases") not overwrite with each iteration of jj (i.e.: so there are jj rows in "phases")? Each row of "phases" will be a different column length (e.g.: for jj = 1 it returns a 1x24 vector, for jj = 2 it returns 1x13 vector). I can't just do below, because the vectors are of different lengths.
phases(jj) = tmp(Bandphase_logical(jj,:))
Is there a way to place NaN to make the vector lengths the same as the matrix is getting populated?
Thank you again!
PK
Stephen Cobeldick on 23 Aug 2018
PAK on 30 Aug 2018
This was amazing. Thank you!!

R2018a

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