CODEWITHSUNDEEP
matlab
Novice_Developer
Novice_Developer

Reputation: 1492

find index of a specific number row wise

Consider the following example 

A =

     6     9     4     7    10
     3     6     5     5     9
    10     4     9     8     6
    10     6     3     4     6
     6     3     3     8     6
     6     4     4     4     5
     5    10     8     5     7
    10    10     8     8     7
     5     7     8     9     9
     3     3     6     3     9

[~,Inx] =max(A, [],2)

Inx =

     5
     5
     1
     1
     4
     1
     2
     1
     4
     5

The above code returns index of the maximum number along each column like in first row the max number is 10 in 5th row so Inx(1) = 5 Can we do the same thing for find ? like for example if I want to find a specific number in each row lets say 8 

>> find(A == 8)

ans =

    27
    28
    29
    33
    35
    38

I will get the indices but not row wise like we get for the max() is there some way to do minipulate find to get that ? or else some other way

Update : I know we can use [row,col,v] = find(___) but there is one problem with that it only returns for the rows where the value is present

Upvotes: 1

Views: 94

Answers (2)

Suever
Suever

Reputation: 65430

You can simply convert A to a logical matrix where it's 1 if equal to 8 and 0 otherwise. Then you can use the second output of max to find the column which contains the first 8 in each row. If a row doesn't contain any 8's the first output of max will be a 0 and the second output will be 1. You can multiply the first and second outputs to zero-out these rows that didn't have an 8.

[has8, col] = max(A == 8, [], 2);

% Zero out any rows that didn't contain an 8
result = has8 .* col;

%   0
%   0
%   4
%   0
%   4
%   0
%   3
%   3
%   3
%   0

If you'd rather have NaN's than 0's, you could do the following which exploits the fact that 0/0 == NaN

result = has8 .* col ./ has8;

%   NaN
%   NaN
%     4
%   NaN
%     4
%   NaN
%     3
%     3
%     3
%   NaN

Upvotes: 3

Steve Heim
Steve Heim

Reputation: 809

Inx = zeros(size(A,1),1); % initialize with default values
[row,col,v] = find(A==8); % find the proper indices
Inx(row) = col; % insert values

Upvotes: 0

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