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To find a vector subset of a matrix in sequence?

Asked by Vishal Sharma on 27 Jan 2017
Latest activity Commented on by Vishal Sharma on 27 Jan 2017
I have a vector A = [1 2 3] And another matrix B = [2 3 4 1; 1 2 3 4; 2 4 1 3; 2 3 1 4]
I want to know which row of vector A is subset of Matrix B (in same sequence of A, i.e. 1 2 3
The answer is 2nd row of B matrix

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Answer by Thibaut Jacqmin on 27 Jan 2017
 Accepted Answer

Here is a solution in one line :
A = [1 2 3];
B = [2 3 4 1; 1 2 3 4; 2 4 1 3; 2 3 1 4];
% Reshape B in a 1D array (all rows in a line)
C = reshape(B', [1, numel(B)]);
% Then use strfind to find a pattern in a string pattern within a string
linear_index = strfind(C, A);
% Compute the row number of the pattern knowing the initial number of columns
row_number = ceil(linear_index/size(B, 2));
% Or do it in a single line :
row_number = ceil(strfind(reshape(B', [1, numel(B)]), A)/size(B, 2));

  2 Comments

Jan
on 27 Jan 2017
A good idea.
The current version fails, if the searched vector appears over the margins:
B = [2 3 4 1; 2 3 1 4]
But you can filter all occurrences, which do not start between 1 and size(B,2)-length(A).
please suggest code for this case

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