[英]Matlab: First Non-zero element of each row or column
For example, 例如,
A = [ -1 0 -2 0 0
2 8 0 1 0
0 0 3 0 -2
0 -3 2 0 0
1 2 0 0 -4];
how can I get a vector of the first nonzero elements of each row? 如何获得每行的第一个非零元素的向量?
You can use max
: 你可以使用
max
:
>> [sel, c] = max( A ~=0, [], 2 );
Rows for which sel
equalse zero - are all zeros and the corresponding column in c
should be ignored. sel
等于零的行 - 全部为零, c
的相应列应该被忽略。
Result: 结果:
>> [sel c]= max( A~=0, [], 2 )
sel =
1
1
1
1
1
c =
1
1
3
2
1
In order to find the first non-zero row index (for each column) you just need to apply max
on the first dimension: 为了找到第一个非零行索引(对于每个列),您只需要在第一个维度上应用
max
:
>> [sel r] = max( A~=0, [], 1 );
Here is a solution based on accumarray that will work even if a row is all zeros. 这是一个基于accumarray的解决方案,即使一行全为零也能工作。
A = [ -1 0 -2 0 0
2 8 0 1 0
0 0 3 0 -2
0 -3 2 0 0
1 2 0 0 -4];
[r,c] = find(A);
%# for every row, take the minimum column index and put NaN if none is found
firstIndex = accumarray(r,c,[size(A,1),1],@min,NaN);
You can do it by executing find function for each row as follows: 您可以通过执行每行的查找功能来执行此操作,如下所示:
A = [ -1 0 -2 0 0
2 8 0 1 0
0 0 3 0 -2
0 -3 2 0 0
1 2 0 0 -4];
% make cell of rows
cellOfRows = num2cell(A, 2);
% apply find function for each row
indexOfFirstNonZeroValues = cellfun(@(row) find(row, 1, 'first'), cellOfRows);
indexOfFirstNonZeroValues =
1
1
3
2
1
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