[英]Find the index of the last non-zero element in each row of a given matrix?
對於任意大小的矩陣x
,如何找到給定矩陣的每一行中最后一個非零元素的索引?
例如,對於矩陣
x = [ 0 9 7 0 0 0; 5 0 0 6 0 3; 0 0 0 0 0 0; 8 0 4 2 1 0 ]
應該獲得向量[ 3 6 0 5 ]
。
這是一個較短的版本,結合了find和accumarray
x = [ 0 9 7 0 0 0; 5 0 0 6 0 3; 0 0 0 0 0 0; 8 0 4 2 1 0 ];
%# get the row and column indices for x
[rowIdx,colIdx] = find(x);
%# with accumarray take the maximum column index for every row
v = accumarray(rowIdx,colIdx,[],@max)'
v =
3 6 0 5
這是一個版本:
x = [ 0 9 7 0 0 0; 5 0 0 6 0 3; 0 0 0 0 0 0; 8 0 4 2 1 0 ];
c = arrayfun(@(k) find(x(k,:)~=0,1,'last'), 1:size(x,1), 'UniformOutput',false);
c( cellfun(@isempty,c) ) = {0};
v = cell2mat(c);
v =
3 6 0 5
編輯 :考慮這個替代解決方案:
[m,v] = max( cumsum(x'~=0) );
v(m==0) = 0;
v =
3 6 0 5
我的回答有點扭曲,但也應該有效
x = [ 0 9 7 0 0 0; 5 0 0 6 0 3; 0 0 0 0 0 0; 8 0 4 2 1 0 ];
[~,pos] = max([fliplr(x~=0),ones(size(x,1))],[],2);
v = size(x,2)-pos' +1;
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