Like function

AIman

I need to use a function that will take something and compare it to the closest match. In this case its a scanner picking up·numbers.

Numbers·will be similar but not the same and the closest matching number is what dictates where things get shipped.

Can the BS2 do this?
·

Mike Green

In principal it can do this. I'm assuming you'll have the scanner provide the information as a string of characters. The issue is: What do you mean by closest match? You will need to define what you mean. Will you have a table of numbers to compare against? How big does the table have to be? How long (big) are the numbers? Do you have to account for missing digits? If there is a table of numbers, how will you define it? How will you install it in the Stamp? How will you update it? If the table is too big, the Stamp may not be able to hold it along with the program. If the rules are too complicated, the Stamp may not be fast enough or may not have enough working memory (variables) to process the rules. What kind of scanner is it? How much time and resources will the Stamp have to devote to running the scanner?

Beau Schwabe

I am pretty sure the stamp would work for you, but you need to give us more information. Your result will ultimately depend on what
kind of matching algorithm you choose, and how you implement it. A common style algorithm is to simply look at how many numbers
match between a known and unknown. That in and of itself could have several implementations.

Example:

10.01.30.40.234 <-- Assume this is the number you want

10.33.36.40.234 <-- Number received


You could say that you have a 60% match because 3 of the 5 numbers match. A more aggressive approach would compare how close
the numbers that did not match were to one another. In this example assuming that 255 is the highest number, you could again look
at the data this way....

(010:010) = 0 ---> 255 - 0 = 255
(001:033) = 32 --> 255 - 32 = 223
(030:036) = 6 ---> 255 - 6 = 249
(040:040) = 0 ---> 255 - 0 = 255
(234:234) = 0 ---> 255 - 0 = 255

255+223+249+255+255 = 1237 ----> 1237 / 1275 = 97%

Note: 1275 = 255 * 5 ... (The maximum value times the number of samples)

Here, the same numbers have a 97% match to one another. So it really depends on how you want to look at your data.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Andy Lindsay (Parallax)

AIman said...
...a function that will take something and compare it to the closest match. In this case its a scanner picking up·numbers....

As far as a function for finding the closest number, yes, the BASIC Stamp can do it.· Here is an example:

' FindClosestValue.bs2
 
' {$STAMP BS2}
' {$PBASIC 2.5}
 
index        VAR   Word
value        VAR   Word
closest      VAR   Word
listItem     VAR   Word
 
DO
 
  closest = 65535
  DEBUG CR, "Enter a value: "
  DEBUGIN DEC value
 
  FOR index = 0 TO 6
    LOOKUP index, [noparse][[/noparse]1, 5, 9, 80, 111, 200], listItem
    IF ABS(value - listItem) <= ABS(closest - value) THEN
      closest = listItem
    ENDIF
  NEXT
 
  DEBUG "Closet entry is: ", DEC closest
 
LOOP

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Andy Lindsay

Education Department
Parallax, Inc.

AIman

Thanks - thats exactly what I needed to know.

Andy Lindsay (Parallax)

For posterity's sake:

The loop in FindClosestValue.bs2 can also be used for sorting packages by size assuming the BASIC Stamp is measuring it with an ultrasonic peripheral such as the Ping))) sensor.·

As Mike Green pointed out, the BASIC Stamp 2 might not have the processing speed to for some sorting situations where the list of values is very large and the speed of the conveyer belt is fast.· In that case, a BASIC Stamp with more speed and/or memory such as the BASIC Stamp 2p or 2px, or even the Propeller chip·might be in order.· External EEPROM memory may also be necessary for storing larger lists.

On the other hand, a BASIC Stamp 2 system on a given conveyer belt node probably doesn't need to store humungous lists.··Each node in an automatic sorting system is typically concerned with a subset of the data on the barcode.· The text or value can be parsed before it is sorted, significantly reducing the decision time.

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Andy Lindsay

Education Department
Parallax, Inc.

Post Edited (Andy Lindsay (Parallax)) : 2/28/2007 7:53:17 PM GMT