Best Method to Categorize objects ( Convert particular words to pre-determined numbers)

Hi,

I have a list of books to be categorized into a pre determined list of categories and they all have different IDs. Example:

Category ID
Arts 1
Engineering 2
Commerce 3
Hobbies 4
etc 5
etc ..
etc ..
etc 100

Now the system requires the books to be categorized and their category IDs be entered in a field. If there are multiple, the multiple values are to be separated by coma. eg: "1,2" ( Arts and Engineering )

The list of the categories goes upto 150. There are thousands of these books to be classified into their categories.

Since the data entry person ( me ) has a good knowledge of the categories, he can manually enter the full name of the category ( with a custom autolist form ) or it will be cumbersome to look up each category's ID. He also knows that there wont be more than 5 categories for a book.

He can either enter all the categories of a book in a cell eg: "Engineering,Commerce" and then run a find and replace for each category. That means he has to do it 150 times to get each category.

Is there any other formula that will automatically convert, say, "Engineering,Commerce" to "2,3" automatically? There is this particular point that all books wont have a fixed number of categories. Some might have just 1. Some might fit into 3 or 4 categories.

Help Please?

Thanks!

P.S. I thought of another method. I get 5 columns ( Category 1, Category 2.... Category 5 ). In these columns, for a book in a row, i type categories separately in each column and i have a 5 other columns that can just convert the information in the previous 5 columns according to their ID. It goes like

6th Column converts 1st Column ( Text ) to ID
7th Column converts 2nd Column ( Text ) to ID
8th Column converts 3rd Column ( Text ) to ID
9th Column converts 4th Column ( Text ) to ID
10th Column converts 5th Column ( Text ) to ID

Then i save the 2nd set of 5 columns in CSV so that i get the IDs separated by coma.

Please advice on this as well.

Thank you so much Cheshire

Is it possible for you to provide a quick summary of what magic you did on the provided spreadsheet?

Once again, thanks!