How to set a condition for sequential number of non NaN values in a vector?

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Ekaterina Serikova
Ekaterina Serikova 2016-5-13
评论： dpb 2016-5-19
Hello, I have a matrix like that:
NaN -0.00042 0.00073 -0.00298 NaN
NaN -0.00114 0.00029 0.00265 NaN
NaN -0.00028 NaN -0.00066 NaN
NaN 0.00197 0.00219 0.00099 NaN
I would like to write a condition for each column: if the number of SEQUENTIAL non-NaN values >=300 (no matter where exactly in a column and non NaNs have not be the same, just any non NaNs), then leave the column, otherwise - delete the whole column. I'm stuck with that "sequential" - how can I say to matlab look for 300 consecutive non-NaNs in a row??
I would appreciate any help.
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dpb
dpb 2016-5-13
Gotta' run; realized I'm late for a meeting...but look for a "runs" submission on FileExchange (maybe Bruno, I forget???).

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采纳的回答

Roger Stafford
Roger Stafford 2016-5-13
编辑：Roger Stafford 2016-5-13
Let M be your matrix.
[m,n] = size(M);
T = diff([true(1,n);isnan(M);true(1,n)],1,1);
T2 = false(1,n);
for k = 1:n
f = find(T(:,k));
T2(k) = any((f(2:2:end)-f(1:2:end-1))>=300); % <-- Corrected
end
M2 = M(:,T2);
M2 will be your result. I assume that where you said "delete" you meant that literally - such columns should be removed from the matrix.
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Ekaterina Serikova
Ekaterina Serikova 2016-5-19
Dear Roger, could you please advise how can I adjust the code for zeroes instead of NaNs? How can I Change isnan condition to zeroes? Thanks a lot.
dpb
dpb 2016-5-19
Should be to just replace isnan(M) with M==0 in the first expression (although you may need to check on the initial condition as as long as there are no NaN in M the first value can't be but might it be 0?

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the cyclist
the cyclist 2016-5-13
Download RunLengths from the FEX.
Then run this code. (I used a length threshold of 3 for illustration. You'll want to use 300.)
LENGTH_THRESHOLD = 3;
M = [NaN -0.00042 0.00073 -0.00298 NaN
NaN -0.00114 0.00029 0.00265 NaN
NaN -0.00028 NaN -0.00066 NaN
NaN 0.00197 0.00219 0.00099 NaN]
numberColumns = size(M,2);
maxNonNanLength = zeros(1,numberColumns);
for nc = 1:numberColumns
[b,L] = RunLength(M(:,nc));
currentNonNanLength = 0;
for nb = 1:numel(b)
if isnan(b(nb))
currentNonNanLength = 0;
else
currentNonNanLength = currentNonNanLength + L(nb);
maxNonNanLength(nc) = max(maxNonNanLength(nc),currentNonNanLength);
end
end
end
hasSufficientNonNanLength = maxNonNanLength >= LENGTH_THRESHOLD;
M = M(:,hasSufficientNonNanLength);

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