MATLAB: Finding first rightmost non-zero column of a matrix

columnfindimageleftmostmatrix

How can I tell MATLAB to find the index of the RIGHTmost non-zero column of said matrix?

I found a similar question and answer for the leftmost column and it worked great! However, I am having trouble finding the rightmost column.

Ex: https://www.mathworks.com/matlabcentral/answers/301099-find-first-non-zero-column-of-a-matrix#answer_232924

I need the leftmost column.

PLS&THANKYOU!

Best Answer

Same solution as the other except search from the other end...

find(any(A),1,'last')

I think Azzi's solution there doesn't find the column positionally but will find the column with the largest number of nonzero elements in it. So

[2 1
 0 1
 0 1]

with his would return 2, not 1 because three rows of second column return T but only one of column 1 will. But both have nonzero elements.

any() does the logical test by column for there being one or more nonzero elements so doesn't matter how many there are as long is one it'll show up. Then the find() locates either first or last depending on which direction you ask for with the optional argument.

Related Solutions

MATLAB: Find first non-zero column of a matrix

>> A=[zeros(5) randn(5)]; A=A(:,randperm(10));  % sample dataset
A =
 -0.7440    1.0223    0   -0.7062   0    0.1257         0    1.2390         0         0
 -0.3744   -1.4192    0   -1.0207   0    0.6963         0    0.8987         0         0
  0.4241    2.5467    0    1.1340   0    1.7395         0   -1.1501         0         0
  0.1141   -0.3580    0    0.0385   0    0.6654         0   -0.2642         0         0
 -0.5111    0.4013    0    0.2309   0    0.6875         0   -1.6252         0         0
>> find(any(A),1)  % first column nonzero
ans =
   1
>>

That one seems too easy; let's try again...

>> A=A(:,randperm(10)); 
A =
       0   -0.7440    0   0    1.0223    1.2390         0         0    0.1257   -0.7062
       0   -0.3744    0   0   -1.4192    0.8987         0         0    0.6963   -1.0207
       0    0.4241    0   0    2.5467   -1.1501         0         0    1.7395    1.1340
       0    0.1141    0   0   -0.3580   -0.2642         0         0    0.6654    0.0385
       0   -0.5111    0   0    0.4013   -1.6252         0         0    0.6875    0.2309
>> find(any(A),1)
ans =
   2
>>

OK, that's more difficult and illustrates it does work as expected...

MATLAB: How to find maximum value within each columns and and return the entire elements in that column

This code seperates A to odd and even elements, and culculates B with logical indexing.

A = [ 0.0596    0.0714    0.8181    0.1499    0.9730    0.4538    0.0835    0.3909;
    0.6820    0.5216    0.8175    0.6596    0.6490    0.4324    0.1332    0.8314;
    0.0424    0.0967    0.7224    0.5186    0.8003    0.8253    0.1734    0.8034];
A_odd = A(:,1:2:end-1);
A_even =A(:,2:2:end);
B = A_odd .* (A_odd > A_even) +A_even .* (A_even > A_odd)

B =

0.0714 0.8181 0.9730 0.3909

0.6820 0.8175 0.6490 0.8314

0.0967 0.7224 0.8253 0.8034

Best Answer

Related Solutions

MATLAB: Find first non-zero column of a matrix

MATLAB: How to find maximum value within each columns and and return the entire elements in that column

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