Replace zero in a matrix with value in previous row
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Hi,
Can you please help me on how can I replace all zeroes in a matrix with the value in previous row?
e.g. if value in row 3 column 4 is 0, it should pick value in row 2 column 4.
I can do it using a for loop but I dont want to use that.
Thanks.
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Réponse acceptée
Azzi Abdelmalek
le 1 Fév 2014
Modifié(e) : Azzi Abdelmalek
le 1 Fév 2014
A=[1 2 3 4;4 5 0 0;1 0 0 1 ;0 1 1 1]
while any(A(:)==0)
ii1=A==0;
ii2=circshift(ii1,[-1 0]);
A(ii1)=A(ii2);
end
4 commentaires
Jan
le 4 Nov 2016
@Mido: Please open a new thread for a new question.
match = (A(:, 3)==0);
A(match, 3) = A(match, 2);
Plus de réponses (5)
Shivaputra Narke
le 1 Fév 2014
Now answer to your comment...
while(all(a(:))) a(find(a==0))=a(find(a==0)-1) end
3 commentaires
Captain Karnage
le 2 Déc 2022
That expression doesn't work as written in a single line. Without a ; after the assignment, it gets an error 'Error: Illegal use of reserved keyword "end".` If I add the ; however, it doesn't error but it still doesn't work. I'm not sure why, because logically it seems like it should, but I just get the original a out when I run it.
DGM
le 3 Déc 2022
Modifié(e) : DGM
le 3 Déc 2022
The loop is never entered at all. You could make some modifications.
a = [0 5 9 13; 2 6 0 0; 3 0 0 15; 0 8 12 16]
na = numel(a);
while ~all(a(:)) % loop runs until there are no zeros
idx = find(a==0);
a(idx) = a(mod(idx-2,na)+1);
end
a
The redundant find() can be removed. Since this is based on decrementing the linear indices, this will fill zeros at the top of a column with content from the bottom of the prior column. Using mod() allows the wrapping behavior to extend across the ends of the array. Note that a(1,1) is filled from a(16,16).
Whether this wrapping behavior is intended or acceptable is a matter for the reader to decide.
Andrei Bobrov
le 1 Fév 2014
l = A == 0;
ii = bsxfun(@plus,size(A,1)*(0:size(A,2)-1),cumsum(~l));
out = A;
out(l) = A(ii(l));
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Shivaputra Narke
le 1 Fév 2014
May be this code can help...
% where a is your matrix a(find(a==0))=a(find(a==0)-1)
2 commentaires
Amit
le 1 Fév 2014
Lets say your matrix is A
[m,n] = size(A);
An = A';
valx = find(~An); % This will give you zeros elements linear index
valx = valx(valx-n > 0);
An(valx) = An(valx-n);
A = An';
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