Difference between revisions of "LlList2ListStrided"

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(→‎Starting at an offset: If you want every second (or third, etc.) item in each stride returned, rather than the first, use llList2ListSlice instead.)
 
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{{LSL_Function/negative index|true|start|end}}{{LSL_Function
{{LSL_Function
|inject-2={{LSL_Function/negative index|true|start|end|noExclude=*}}{{LSL_Function/stride|stride}}
|func_id=198|func_sleep=0.0|func_energy=10.0
|func_id=198|func_sleep=0.0|func_energy=10.0
|func=llList2ListStrided
|func=llList2ListStrided
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|func_footnote
|func_footnote
|func_desc
|func_desc
|return_text=of all the entries in the [[List#Strided_lists|strided list]] whose index is a multiple of '''stride''' in the range '''start''' to '''end'''.
|return_text=of all the entries in the [[List#Strided_lists|strided list]] whose index is a multiple of {{LSLP|stride}} in the range {{LSLP|start}} to {{LSLP|end}}.
|spec
|spec
|caveats
|caveats
|constants
|constants
|examples=
|examples=
<lsl>list mylist = [0,1,2,3,4,5,6];
<source lang="lsl2">list mylist = [0,1,2,3,4,5,6];
list result_a = llList2ListStrided(mylist,0,-1,2); //start at first item in list, go to the end, return every 2nd item
list result_a = llList2ListStrided(mylist,0,-1,2); //start at first item in list, go to the end, return every 2nd item
//result_a == [0,2,4,6]
//result_a == [0,2,4,6]
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list result_c = llList2ListStrided(mylist,2,-1,2); //start at third item in list, go to the end, return every 2nd item
list result_c = llList2ListStrided(mylist,2,-1,2); //start at third item in list, go to the end, return every 2nd item
//result_c == [2,4,6]</lsl>
//result_c == [2,4,6]</source>


<lsl>list menu = ["1", "one", "2", "two", "3", "three"];
<source lang="lsl2">list menu = ["1", "one", "2", "two", "3", "three"];
default
default
{
{
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         }
         }
     }
     }
}</lsl>
}</source>


|helpers
|helpers
|also_functions=[[User:Fred_Gandt/Scripts/Functions#StrideOfList_.28_V2_.29|StrideOfList]] - '''User created function''' performing a similar task (in case you are not getting the results you want from llList2ListStrided).
|also_functions=
{{LSL DefineRow||[[llList2ListSlice]]|}}
 
|also_events
|also_events
|also_tests
|also_tests
|also_articles
|also_articles
|notes=  
|notes=  
To get every first element in a "collection of data" in a strided list:
=== Starting at an offset ===
 
If you want every second (or third, etc.) item in each stride returned, rather than the first, use [[llList2ListSlice]] instead.
<lsl>list ListStridedFirstElement(list src, integer start, integer end, integer stride) {
    return llList2ListStrided(llList2List(src, start, end), 0, end, stride);
}</lsl>
 
To get every second element in a "collection of data" in a strided list:
 
<lsl>llList2ListStrided(llDeleteSubList(src, 0, 0), 0, -1, 3);</lsl>
 
|permission
|permission
|negative_index
|negative_index
|haiku={{Haiku|Ah, the strided list.|C had structs in the '70s.|Someday, we will, too...}}
|sort=List2ListStrided
|sort=List2ListStrided
|cat1=List
|cat1=List

Latest revision as of 11:46, 25 October 2023

Summary

Function: list llList2ListStrided( list src, integer start, integer end, integer stride );
0.0 Forced Delay
10.0 Energy

Returns a list of all the entries in the strided list whose index is a multiple of stride in the range start to end.

• list src
• integer start – start index
• integer end – end index
• integer stride – number of entries per stride, if less than 1 it is assumed to be 1

This function supports Strided Lists.

Specification

Index Positive Negative
First 0 -length
Last length - 1 -1

Indexes

  • Positive indexes count from the beginning, the first item being indexed as 0, the last as (length - 1).
  • Negative indexes count from the far end, the first item being indexed as -length, the last as -1.

Caveats

  • If either start or end are out of bounds the script continues to execute without an error message.
  • start & end will not form an exclusion range when start is past end (Approximately: start > end), instead it will act as if start was zero & end was -1.

Examples

list mylist = [0,1,2,3,4,5,6];
list result_a = llList2ListStrided(mylist,0,-1,2); //start at first item in list, go to the end, return every 2nd item
//result_a == [0,2,4,6]

list result_b = llList2ListStrided(mylist,1,-1,2); //start at second item in list, go to the end, return every 2nd item
//result_b == [2,4,6]

list result_c = llList2ListStrided(mylist,2,-1,2); //start at third item in list, go to the end, return every 2nd item
//result_c == [2,4,6]

list menu = ["1", "one", "2", "two", "3", "three"];
default
{
    state_entry()
    {
        llListen(10, "", llGetOwner(), "");
    }
    touch_start(integer detected)
    {
        list buttons = llList2ListStrided(menu, 0, -1, 2);
        llDialog(llDetectedKey(0), "choose a number", buttons, 10);
    }
    listen(integer channel, string obj, key id, string message)
    {
        integer index = llListFindList(menu, [message]);
        if (index != -1)
        {
            llOwnerSay("you chose " + llList2String(menu, index + 1) + " (" + message + ")");
        }
    }
}

Notes

Ranges & Indexes

The easiest way to explain how ranges work is to make all indexes positive. Negative indexes are just a way of counting from the tail end instead of the beginning, all negative indexes have a corresponding equivalent positive index (assuming they are in range). Positive indexes past length (after the last index), or negative indexes past the beginning (before the first index) are valid and the effects are predictable and reliable: the entries are treated as if they were there but were removed just before output.

  • If start <= end then the range operated on starts at start and ends at end. [start, end]
  • Exclusion range: If start > end then the range operated on starts at 0 and goes to end and then starts again at start and goes to -1. [0, end] + [start, -1]
    • If end is a negative index past the beginning, then the operating range would be [start, -1].
    • If end is a positive index past the end, then the operating range would be [0, end].
    • If both start and end are out of bounds then the function would have no operating range (effectively inverting what the function is supposed to do).

See negative indexes for more information.

Starting at an offset

If you want every second (or third, etc.) item in each stride returned, rather than the first, use llList2ListSlice instead.

See Also

Functions

•  llList2ListSlice

Articles

•  Negative Index

Deep Notes

Signature

function list llList2ListStrided( list src, integer start, integer end, integer stride );

Haiku

Ah, the strided list.
C had structs in the '70s.
Someday, we will, too...

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