changing values in a certain column of a matrix

I have a large matrix and in the fifth column I want to replace every value of 990 with 30.375, how could I do this easily? I found many similar questions but not exactly the same one and I tried to adapt the solutions to my situation but it hasn't worked yet..

Answer 1

[Cedric]

First, you build a logical index of all values equal to 990 in column 5:

 lId = A(:,5) == 990 ;

Then you use it to index relevant elements of A (in column 5), that you set to 30.375:

 A(lId,5) = 30.375 ;

Let me know if you need more information.

[Evelyn]

Yes! That works! Thank you so much. I ended up with:

A( A (:,5) == 990,1) = 30.375;

any idea why that didn´t work? (I am already very glad I have it working now, but I'm just asking in an attempt to learn even more from my mistakes)

[Cedric]

Almost correct. The outcome of the expression

 A(:,5) == 990

is what I stored in the intermediary variable lId. It is a column vector of logicals which are true where A(:,5) is equal to 990 and false otherwise. You can use the expression directly for indexing (logical indexing) rows of A (along the first dimension), but you still have to index the correct column, i.e. column 5:

 A( A(:,5)==990, 5 ) = 30.375 ;

[Image Analyst]

Welcome back Cedric. It seems like you took a sabbatical for a few months.

[Cedric]

Thank you Image Analyst! Yes, I could have warned, but I always thought that I would be able to come back "within a few days", and I lost track of time!

[Dogiparthi Santhosh Gupta]

Is the same logic applicable on a table with single column.

My problem is 'I have to replace the values of 2,3,4 in a single column of a table to 1' I tried with your logic but getting an error. Kindly suggest the perfect logic by anyone.

Answer 2

[sayem sujon]

Change the value of the 3rd column to [6 9 2 5]