MATLAB: How to find first ‘1’ in every row

find

Hi,

I have a matrix,

A = [ 0 0 0 0 0 0 1 1 1 1 0 0; 0 0 0 0 0 1 1 1 1 0 0 0; 0 0 0 0 0 0 1 1 1 1 0 0]

My question is, how to find the first '1' in each row. I want the output will show like this:

B = [7; 6; 7]

Meaning that, for the first row, the number 1 found on column number 7, second row found in column number 6 and so on.

Thank you in advance for any answered

Best Answer

 [~,B]=max(A,[],2);

Related Solutions

MATLAB: How to place a cell array in another cell array using ‘find’

If I understood correctly:

Ax = randi([0 1], 4, 960);  %Demo data. No way I'm reformating your example to make it valid matlab syntax. 
[row, col] = find(A);
blockidx = discretize(col, 1:60:size(A, 2));
Bx = accumarray([row, blockidx], col, [], @(c) {sort(c).'})

Note: I'm not working on the whole cell array here, just one of these 4x960 matrix as I've not understood what that had to do with the question. Possibly, you just want to above in a loop (or cellfun) operating over each element of the cell array.

MATLAB: Does deleting a cell array of anonymous references with input arguments take longer than deleting the same array if the references have no input arguments in MATLAB 7.7 (R2008b)

The reason behind the slowdown is the cyclic references made by the function handles to each other indirectly through the parent workspace that holds the cell array. While deleting these handles, a lot of the time is spent in resolving these cyclic references and hence the delay in the performance.

This limitation can be worked around by creating a nested function with no arguments referring to the workspace.

Below is an illustrative example:

function fnTest(N)
fprintf('% s \n','no inputs')
tic; a=cell(N,1); for k = 1:N, a{k} = @sum; end, toc;
tic; clear a; toc;
fprintf('% s \n','Anonymous function with values from the workspace')
y=1;
tic; b=cell(N,1); for k = 1:N, b{k} = @(x)sum(x,y); end, toc;
tic; clear b; toc;
fprintf('% s \n','function handle to a nested function')
y =1;
tic; c = cell(N,1); for k = 1:N, c{k} = @(x)sum2(x); end, toc;
tic; clear c; toc;
     % nested functions have access to the workspaces of all functions in
     % which it is nested.  In this case it means that sum2 can "see" y, but
     % it will not create a reference like an anonymous function will.
     function out = sum2(x)
         out = sum(x,y);
     end
end

This code results in the following timings:

 >> fnTest(25000)
 no inputs 
 Elapsed time is 0.074842 seconds.
 Elapsed time is 0.238302 seconds.
 Anonymous function with values from the workspace 
 Elapsed time is 1.042215 seconds.
 Elapsed time is 6.881813 seconds.
 function handle to a nested function 
 Elapsed time is 0.995948 seconds.
 Elapsed time is 0.646475 seconds.

Best Answer

Related Solutions

MATLAB: How to place a cell array in another cell array using ‘find’

MATLAB: Does deleting a cell array of anonymous references with input arguments take longer than deleting the same array if the references have no input arguments in MATLAB 7.7 (R2008b)

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