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Find the index of first and last non zero in column

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Teerapong Poltue
Teerapong Poltue 2021-6-2
评论： Chunru 2021-6-2
I got the array as shown
I would like to extract the index (idx) of the first and last non zero in column, how can I do that.
The expected return of the code is
data(idx_first) = [1 1 2]
data(idx_last) = [1 5 5]

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采纳的回答

Chunru
Chunru 2021-6-2
x = [0 1 0 4; 1 2 0 1; 0 1 2 0; 0 0 0 0]
[m, n] = size(x);
ind = zeros(1, n);
for i=1:n
xlast = find(x(:, i), 1, 'last');
ind(i) = sub2ind([m n], xlast, i);
end
x(ind)
  2 个评论
Teerapong Poltue
Teerapong Poltue 2021-6-2
ther's a tiny problem on this code when the colum is entire 0, it caused error in sub2ind. How can I solve that?
Chunru
Chunru 2021-6-2
[m, n] = size(x);
ind = nan(1, n);
for i=1:n
xlast = find(x(:, i), 1, 'last');
if ~isempty(xlast)
ind(i) = sub2ind([m n], xlast, i);
end
end
y = zeros(1,n);
ind0 = ~isnan(ind);
y(ind0) = x(ind(ind0))

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更多回答（1 个）

KSSV
KSSV 2021-6-2
Ran in:
A = [0 89 90 0 99 100 0] ;
id1 = find(A,1,'first')
id1 = 2
id2 = find(A,1,'last')
id2 = 6

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