LOOKUP Index, (Value0, Value1, ...ValueN),
Syntax : LOOKUP Index, [Value0, Value1, ...ValueN], Variable
Find the value at location Index and store it in Variable. If Index exceeds the highest index value of the items in the list, Variable is left unaffected.
* Note: expressions are not allowed as arguments on the BS1.
|All BASIC Stamp Modules|
|Limit of value entries||256|
|Starting index number||0|
|If index exceeds the highest location...||Variable is left unaffected|
LOOKUP retrieves an item from a list based on the item's position, Index, in the list. For example:
SYMBOL idx = B2 SYMBOL result = B3 Setup: idx = 3 result = 255 Main: LOOKUP idx, (26, 177, 13, 1, 0, 17, 99), result DEBUG "Item ", #idx, "is: ", #result END
idx VAR Nib result VAR Byte Setup: idx = 3 result = 255 Main: LOOKUP idx, [26, 177, 13, 1, 0, 17, 99], result DEBUG "Item ", DEC idx, " is: ", DEC result END
In this example, DEBUG prints "Item 3 is: 1." Note that the first location number is 0. In the list above, item 0 is 26, item 1 is 177, etc.
If Index is beyond the end of the list, the result variable is unchanged. In the example above, if index were greater than 6, the message would have reported the result to be 255, because that's what result contained before LOOKUP executed.
Don't forget that text phrases are just lists of byte values, so they too are eligible for LOOKUP searches, as in this example:
SYMBOL idx = B2 SYMBOL result = B3 Setup: idx = 16 result = "*" Main: LOOKUP idx, ("The quick brown fox"), result DEBUG @result END
iidx VAR Byte result VAR Byte Setup: idx = 16 result = "*" Main: LOOKUP idx, ["The quick brown fox"], result DEBUG ASC? result END
DEBUG prints, "Result = 'f'" because the character at index item 16 is "f" in the phrase, "The quick brown fox".
The examples above show LOOKUP working with lists of constants, but it also works with variables and expressions also. Note, however, that expressions are not allowed as argument on the BS1.
A great use of LOOKUP is in combination with LOOKDOWN to "map" non-contiguous sets of numbers together. For example, you may have an application where certain numbers are received by the BASIC Stamp and, in response, the BASIC Stamp needs to send a specific set of numbers. This may be easy to code if the numbers are contiguous, or follow some know algebraic equations… but what if they don't? The table below shows some sample, non-contiguous inputs and the corresponding outputs the BASIC Stamp needs to respond with:
|Index||Each of these values received (inputs):||Needs to result in each of these values sent (outputs):|
So, if we receive the number 5, we need to output 16. If we received 43, we need to output 24, and so on. These numbers are not contiguous and they don't appear to be derived from any simple algorithm. We can solve this problem with two lines of code, as follows:
LOOKDOWN value, [5, 14, 1, 43, 26, 22, 30], value LOOKUP value, [16, 17, 18, 24, 10, 12, 11], value
Assuming our received number is in value, the first line (LOOKDOWN) will find the value in the list and store the index of the location that matches back into value. (This step "maps" the non-contiguous numbers: 5, 14, 1, etc, to a contiguous set of numbers: 0, 1, 2, etc). The second line (LOOKUP) takes our new value, finds the number at that location and stores it back into value. If the received value was 14, LOOKDOWN stores 1 into value and LOOKUP looks at the value at location 1 and stores 17 in value. The number 43 gets mapped to 3, 3 gets mapped to 24, and so on. This is a quick and easy fix for a potentially messy problem!
BASIC Stamp Help Version 2.5.4
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