How do I delete a row in a matrix where the first value isn't in a corresponding matrix?

I have 2 tables like this:

table files:

| id | ....
------------
| 1  | ....
| 2  | ....
| 7  | ....
| 9  | ....
table blob:

| fileid | ....
------------
| 1  | ....
| 2  | ....
| 3  | ....
| 4  | ....
| 5  | ....
| 7 | ....
| 9  | ....

The tables fileid and id columns can be used to join the tables together.

How do I delete columns 3 4 5. Keep in mind this is only a simple example, I have a data set that contains thousands of rows

Answer 1

[Thorsten]

Create a logical index that has a 1 at each position where fileid has no match in id:

idx = ~ismember(fileid, id);

Delete the corresponding rows in your matrix A:

 A(idx,:) = [];

[Humblespud]

Could you elaborate a bit more please? I am relatively new to Matlab.

[Thorsten]

Sorry. I've updated my answer.

Answer 2

[Image Analyst]

Try intersect() to find numbers that are common to both.

commonNumbers = intersect(fileid{:,1}, id{:,1});

Then use ismember() to find out where the numbers in commonNumbers occur in each table, say these are called rows1 and rows2.

Then use innerjoin():

newTable = innerjoin(fileid({rows1,1}, id{rows2,1});

Or something like that - that's untested, just off the top of my head. Or maybe you want outerjoin()???