What does the 'i' mean in [y,i] = unique(A)?

If I got a m x 1 matrix and I perform this little piece of code in Matlab it returns two arrays 'y' and 'i', where 'y' holds the unique numbers en 'i' holds the row numbers of the unique numbers? I don't understand why this is. Can someone explain this to me?

Answer 1

[Star Strider]

It’s the index into ‘A’, so that ‘y=A(i)’. It returns the index of the first instance of the unique values. If you want all of them (indirectly), you have to ask for the third argument as well.

[Igor Batoukhtine]

What's the difference between the first instance and all of them? I was reading on the vector index page, but I couldn't find this explained. Thanx for your first answer though.

[Star Strider]

My pleasure.

There is no difference if all of the values are unique, and all are already in ascending sorted order.

I don’t know what you intend by ‘the vector index page’. I would refer you to the documentation on the unique function, specifically Unique Values and Their Indices for the details.

[Igor Batoukhtine]

Aaaah great, thanx! I was looking at the wrong page:

Matrix Indexing in Matlab

[Star Strider]

My pleasure!

That isn’t the ‘wrong’ page, and is definitely worth reading (I wish more posters here read it), but not the one that would provide the information you need to understand the unique function.