Difference between revisions of "Category:LSL List"
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Revision as of 08:21, 13 July 2008
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A list is a special kind of data type which can contain zero or more elements.
Lists are signified by square brackets surrounding their elements; the elements inside are separated by commas.
(Note: to be clear for those who have other programming backgrounds, there are no arrays in LSL: only lists.)
Diverse Data Types
Not all elements in a list need to be the same type of element. In the same list, you can store strings, integers, floats, vectors, etc, right side by side.
Example: //a list with an integer, a float, a string, and a vector.
[1,14.154,"Isn't this fun?",<0,0,0>]
However, a list may not contain another list (i.e. you can't nest them.)
[1, "one", 2, "two"] + [3, "three"] returns [1, "one", 2, "two", 3, "three"] not [1, "one", 2, "two", [3, "three"]]
When you add an element to a list, the list remembers automatically what data type the value was.
Generally, because you're the one adding something to a list, you know what datatype is in what place in the list, and you retrieve it out of the list with the appropriate llList2<type> function such as: llList2String, llList2Vector, etc. (more on this later.)
If for some reason, though, you need to test what data type an element is in a list, you can use the llGetListEntryType function.
Tip! When adding a float to a list, always add it with a decimal point (e.g 1.0 as opposed to 1) to ensure that it is preserved as a float.
Counting place in a list vs list length
It's important at the outset to note the following (which can trip up even experienced minds when they are battle-weary):
The length of this list is 3, because it has 3 elements in it.
BUT, counting to determine an element's place in its list (aka "indexing") starts at 0 -- NOT 1.
The position of "Yes" in the above list is 0, "No" is at position 1, and "Perhaps" is at position 2.
Consequently, if you have 7 elements in a list, the last item in the list will be at position 6.
While a script is running, a list can grow dynamically as large as needed, limited only by the amount of memory that is available in the script.
However, at compile (aka save) time, there is a 72 element limit to pre-defined lists hardcoded in the script. Such long, predefined lists are common, for example, when someone is offering the user a plethora of colour choices.
Tip! If you really need 72 or more such choices in a pre-defined list, just make 2 (or more) lists that don't upset the compiler, and join them together in state_entry() or wherever appropriate:
biggerlist = biglist01 + biglist02;
Joining Lists (aka Concatenation)
Lists can be joined simply by using the + sign:
newlist = list01 + list02;
newlist = list01 + ["red","brown",<0,0,0>];
One common use of lists is to duplicate the functionality of structs, structured collections of data, which are available in many programming languages but not in LSL. As an example, you might use a list to track the names, gender and rezzdates of a group of avatars:
["John Adams", "male", "2007-06-22", "Shirley Bassey", "female", "2005-11-02", "Matt Damon", "male", "2008-05-19"]
This example has a stride of three, because the instance has three data elements. Index 0 ("John Adams") is the start of the first instance, index 3 ("Shirley Bassey") is the start of the second instance, and so on.
It is important that the types of information are always entered in the same sequence for every instance in the list! i.e. in this case that the name is always entered first. You should consider carefully the order in which you record information because the function to sort a list, llListSort, will only sort on the first element of the instances. In other words, if the avatar's rezzdate was the most important attribute for your script, then you would need to record it first, and the name second.
Extended List Operations
These functions have been created and contributed by LSL users to perform operations not covered by built-in LSL functions.
|ListItemDelete||Removes one element from a list.|
|ListStridedUpdate||Updates part of a strided list.|
|ListToWholeNumbers||Given a list of floats, converts them all to whole numbers (aka integers.)|
|ListXorY||Join two lists to make one new combined list, while also eliminating any resulting duplicates in the new list.|
|ListXandY||This function examines two lists, and returns a new list composed of the elements that both lists have in common.|
|ListXnotY||Show what x list has that y list is missing.|
|ListXxorY||Returns a new list, composed of elements that were in either original script, but not both. Note: This is not the same as getting rid duplicates by preserving just one of each duplicated item. It goes further, and removes both items.|
|ListXequY||Answers the question: is list X identical to list Y?|
|ListXneqY||Answers the question: is list X different from list Y?|
|Replace||Replaces a single occurrence of something in a list with something else that you specify.|
|Replace All||Replaces all occurrences of 'from list' with those in 'to list' in 'src list'. Not as concise as the replace function above, but will handle multiple items at the same time.|
|ListUnique||Given a list of elements, returns a list of only the unique individual elements in that list.|
This category has the following 5 subcategories, out of 5 total.
Pages in category "LSL List"
The following 27 pages are in this category, out of 27 total.