add different number of zeros in the beginning of a matrix

Question

Praveen Verma 2021-7-20

0
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https://ww2.mathworks.cn/matlabcentral/answers/882108-add-different-number-of-zeros-in-the-beginning-of-a-matrix

回答： Jan 2021-7-20

suppose i have two matrix

A=[1

3

2]

the row index of 1 is 1, 3 is 2 and 2 is 3.

S=[2 3 4 5 6

4 6 8 9 1

2 3 4 5 6

6 5 4 2 1

4 6 8 9 1

2 3 4 5 6 ]

Now i want to insert zeros in the beginning of each row of S. The number of zeros in each row depends upon the index of matrix A and number of rows in which i want to insert zeros depends upon element value matrix A.

For example in matrix A row index of 1 is 1 and value of element is 1 so i want to insert one zero at the beginning of first row of matrix S. Similary in matrix A the row index of 3 is 2 and element value is 3 so i want to insert 2 zeros in next 3 rows (second third and fourth ) in the beginning of matrix S. again in matrix A the row index of 2 is 3 and element value is 2 so i want to insert 3 zeros in next 2 rows (fifth and sixth) in the beginning of matrix S.

finally the result will look like this

S=[0 2 3 4 5 6

0 0 4 6 8 9 1

0 0 2 3 4 5 6

0 0 6 5 4 2 1

0 0 0 4 6 8 9 1

0 0 0 2 3 4 5 6 ]

my actual matrix is very large so plz provide a general solution.

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Dyuman Joshi 2021-7-20

It is not possible to make such a numeric array (of irregular size). You can check it by actually copy-pasting on matrix S and it will give you an error.

However, You can make a cell array (if that is an acceptable answer)

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Answer 1

Jan 2021-7-20

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/882108-add-different-number-of-zeros-in-the-beginning-of-a-matrix#answer_750638

The output cannot be a matrix, as Dyuman Joshi told you already, because in a matrix all rows must have the same number of elements. With a cell vector:

A = [1; 3; 2];
S = [2 3 4 5 6; ...
     4 6 8 9 1   ; ...
     2 3 4  5 6 ; ...
     6 5 4 2 1; ...
     4 6 8 9 1   ; ...
     2 3 4  5 6 ];
nZ     = repelem(1:numel(A), A);
nS     = size(S, 1);
Result = cell(nS, 1);
for k = 1:nS
   Result{k} = [zeros(1, nZ(k)), S(k, :)];
end