Searching for Unique Values

[Steve Etter]

Hi everybody. I'm working with RSLogix5000 and looking to create a database of part numbers and corresponding critical values. To use this database, I will have a PanelView Plus touchscreen where the operator will be able to input new part numbers & values and store them.

My question is this - When the operator triggers the "Store" command, I would like for the program to compare the new part number with all the existing part numbers already entered into the database. How would you do this?

Obviously I could write some down-and-dirty code of many similar compare rungs that look at each part number separately, but I was hoping someone might have an elegant solution.

Thanks in advance,
Steve

 

[Ron Beaufort]

take a look at the FAL and the FSC instructions ... depending on what you decide to do if the numbers DO match - or do NOT match - one of these might be helpful ...

 

[Peter Nachtwey]

A linear search is the the brute force way.

It will work if your data base isn't too big. I would try this first but.....

I would consider using a hash function to generate a hash code or index that is big enough to access your whole data base. I would round this up to a power of two.

A hash function takes the part number and converts it do a hash code or index. The index is then used to access the data base as if it is an array of UDTs.

The trick is to get the right hash function that will generate unique codes or indexes. I usually use an XOR function to generate the hash code.

 

[Steve Etter]

Thanks, guys. Fortunately I have a pretty small list of numbers (less than 50) and each number is only 6 digits long.

Let me take a look at the FAL and FSC instructions and I will get back to let everyone know what I come up with.

Steve