Replace values in matrix by first non-zero value in previous row

2018 3 5
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更新时间：2019 6 21
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Hi, how can i replace zero values in a matrix by the first occurring non-zero value in that matrix if you would loop backwards in each column? I.e. how can i carry forward a value as long as its next value in the same column is zero (without looping through each value in the matrix!)
Example: m_start = [3;0;0;4;0;5] replace_non_zero_values (m_start) = [3;3;3;4;4;5]
Hope you can help, thanks very much! Steven

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Stephen23
Stephen23 2018-3-5
编辑：Stephen23 2018-3-5

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>> M = [3;0;0;4;0;5];
>> idx = M~=0;
>> tmp = M(idx);
>> tmp(cumsum(idx))
ans =
3
3
3
4
4
5
Note this assumes that the first value is nonzero. You will need to think of how to deal with leading zeros!

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Could you help me with implementing this for a matrix? i.e. for M = [3 4;0 2;0 0;5 0] which should result in M_adj = [3 4; 3 2; 3 2;5 2]
thanks!
have to come up with a solution if a value in first row is 0, in that case we need to override this with 1 in the idx matrix...otherwise M(idx) gives error message. 0 in first row also needs to be carried forward until a non-zero value appears.
Guillaume
Guillaume 2018-3-5
编辑：Guillaume 2018-3-5
idx = M(:) ~= 0
tmp = M(idx);
reshape(tmp(cumsum(idx)), size(M))
As with the original answer, this will go badly wrong if any column starts with a 0.
Arturo Camacho Lozano
编辑：Arturo Camacho Lozano 2019-6-21
Stephen's solution is very clever. Thanks!

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