Find the rows with specific value for each column

Hello, I have a 37*10000 matrix, called matrix A.

For each column, I want to get the rows which has a certain value, let's say, 1.

I know how to do with a certain column, by using find, like: find(any(A(:,1)==1,2)). But here, I need to find such rows for all columns, and the number of column is huge. So I dont know how to deal with it?

And is there any way to deal with it without using loop, since the number of column is huge, I am afraid that using loop might take a lot of time to run the command.

Thanks a lot!

Answer 1

[madhan ravi]

a=randi([1 10],4,10)

[row,col]=find(ismember(a,10));

col %represents in which column the value is

[heidi pham]

Thank you! If I understand your answer correctly, it seems that you are finding the column which has value 1.2, in the first row?

I actually want to find for each column, the row that has a specific value (like 1.2 for instance).

Sorry if i misunderstood your point.

[madhan ravi]

No you will get which columns has that value and instead of 1 if you use the iterator for instance i which goes from 1 to 37( meaning row numbers in this case) you will be able to find columns having the value

[heidi pham]

Thanks, it works if I want to get which column, but actually I want to know which rows that has a certain value for each column. So I will need to do iteration for 1 million times, and it is quite tedious...

[madhan ravi]

Or use ismember()

[madhan ravi]

See the edited answer now , you can get rid of loops and ismember is more efficient

[heidi pham]

thanks, i will check it!

[madhan ravi]

Sure thing!

Answer 2

[Akira Agata]

Another possible solution.

A = randi([1 10],4,10);

idx = any(A == 1); % Represents column index in which the value 1 is
col = find(idx);   % Represents column number in which the value 1 is