Second Life Wiki - User contributions [en]

ListUnique

2025-10-13T20:29:56Z

Lachesis Ethereal: /* Function: list ListSortedAndUnique(list {{LSL Param|input}}, integer {{LSL Param|ascending}}) */ typo

{{LSL Header}} __NOTOC__

<div id="box">
== Function: [[list]] ListUnique([[list]] {{LSL Param|lAll) }}; ==
<div style="padding: 0.5em;">
Given a list of elements, strips out any duplicates in that list, and returns the de-duped list.

See also: [[List|Lists]]

<source lang="lsl2">
list ListUnique( list lAll ) {
integer i;
list lFiltered = llList2List(lAll, 0, 0);
integer iAll = llGetListLength( lAll );
for (i = 1; i < iAll; ++i) {
if ( llListFindList(lFiltered, llList2List(lAll, i, i) ) == -1 ) {
lFiltered += llList2List(lAll, i, i);
}
}
return lFiltered;
}

</source>

Example:<br />

list mylist = ListUnique(["A", "A", "B", "C", "C", "B"])

would return the list:

["A", "B", "C"]

</div>

Originated in a November 2004 thread led by Chromal Brodsky in the SL Scripting Forum. http://forums-archive.secondlife.com/54/30/28137/1.html

</div>

<div id="box">
== Function: [[list]] ListSortedAndUnique([[list]] {{LSL Param|input}}, [[integer]] {{LSL Param|ascending}}) ==
<div style="padding: 0.5em;">

If you don't need to maintain the order of items (or want them sorted anyway), the following code is consistently about 2x faster on short lists, and 3-5x faster on lists with hundreds of items.

<source lang="lsl2">list ListSortedAndUnique(list input, integer ascending) {
input = llListSort(input, 1, ascending);
integer index;
list last = llList2List(input, 0, 0);
list result = last;
for (index = 1 - llGetListLength(input); index < 0; ++index) {
list current = llList2List(input, index, index);
if (llListFindList(current, last) < 0) {
last = current;
result += last;
}
}
return result;
}
</source>
</div>

The reason is that [[llListFindList]] performs a linear scan through the entire list, thus ListUnique compares every element with every other element. [[llListSort]] however compares each element only to a few others (the exact number depending on the sorting algorithm), and after sorting ListSortedAndUnique only compares neighboring elements.

</div>
{{LSLC|Examples|ListUnique}}
{{LSLC|Examples|ListSortedAndUnique}}
[[Category:LSL_User-Defined Functions]]

ListUnique

2025-10-13T20:29:33Z

Lachesis Ethereal: /* Function: list ListSortedAndUnique(list {{LSL Param|input}}, integer {{LSL Param|ascending}}) */ The reason is that llListFindList performs a linear scan through the entire list ...

{{LSL Header}} __NOTOC__

<div id="box">
== Function: [[list]] ListUnique([[list]] {{LSL Param|lAll) }}; ==
<div style="padding: 0.5em;">
Given a list of elements, strips out any duplicates in that list, and returns the de-duped list.

See also: [[List|Lists]]

<source lang="lsl2">
list ListUnique( list lAll ) {
integer i;
list lFiltered = llList2List(lAll, 0, 0);
integer iAll = llGetListLength( lAll );
for (i = 1; i < iAll; ++i) {
if ( llListFindList(lFiltered, llList2List(lAll, i, i) ) == -1 ) {
lFiltered += llList2List(lAll, i, i);
}
}
return lFiltered;
}

</source>

Example:<br />

list mylist = ListUnique(["A", "A", "B", "C", "C", "B"])

would return the list:

["A", "B", "C"]

</div>

Originated in a November 2004 thread led by Chromal Brodsky in the SL Scripting Forum. http://forums-archive.secondlife.com/54/30/28137/1.html

</div>

<div id="box">
== Function: [[list]] ListSortedAndUnique([[list]] {{LSL Param|input}}, [[integer]] {{LSL Param|ascending}}) ==
<div style="padding: 0.5em;">

If you don't need to maintain the order of items (or want them sorted anyway), the following code is consistently about 2x faster on short lists, and 3-5x faster on lists with hundreds of items.

<source lang="lsl2">list ListSortedAndUnique(list input, integer ascending) {
input = llListSort(input, 1, ascending);
integer index;
list last = llList2List(input, 0, 0);
list result = last;
for (index = 1 - llGetListLength(input); index < 0; ++index) {
list current = llList2List(input, index, index);
if (llListFindList(current, last) < 0) {
last = current;
result += last;
}
}
return result;
}
</source>
</div>

The reason is that [[llListFindList]] performs a linear scan through the entire list, thus ListUnique compares every element with every other element. [[llSort]] however compares each element only to a few others (the exact number depending on the sorting algorithm), and after sorting ListSortedAndUnique only compares neighboring elements.

</div>
{{LSLC|Examples|ListUnique}}
{{LSLC|Examples|ListSortedAndUnique}}
[[Category:LSL_User-Defined Functions]]

ListUnique

2025-10-13T20:17:35Z

Lachesis Ethereal: /* Function: list ListSortedAndUnique(list {{LSL Param|input}}, integer {{LSL Param|ascending}}) */ fix typo

{{LSL Header}} __NOTOC__

<div id="box">
== Function: [[list]] ListUnique([[list]] {{LSL Param|lAll) }}; ==
<div style="padding: 0.5em;">
Given a list of elements, strips out any duplicates in that list, and returns the de-duped list.

See also: [[List|Lists]]

<source lang="lsl2">
list ListUnique( list lAll ) {
integer i;
list lFiltered = llList2List(lAll, 0, 0);
integer iAll = llGetListLength( lAll );
for (i = 1; i < iAll; ++i) {
if ( llListFindList(lFiltered, llList2List(lAll, i, i) ) == -1 ) {
lFiltered += llList2List(lAll, i, i);
}
}
return lFiltered;
}

</source>

Example:<br />

list mylist = ListUnique(["A", "A", "B", "C", "C", "B"])

would return the list:

["A", "B", "C"]

</div>

Originated in a November 2004 thread led by Chromal Brodsky in the SL Scripting Forum. http://forums-archive.secondlife.com/54/30/28137/1.html

</div>

<div id="box">
== Function: [[list]] ListSortedAndUnique([[list]] {{LSL Param|input}}, [[integer]] {{LSL Param|ascending}}) ==
<div style="padding: 0.5em;">

If you don't need to maintain the order of items (or want them sorted anyway), the following code is consistently about 2x faster on short lists, and 3-5x faster on lists with hundreds of items.

<source lang="lsl2">list ListSortedAndUnique(list input, integer ascending) {
input = llListSort(input, 1, ascending);
integer index;
list last = llList2List(input, 0, 0);
list result = last;
for (index = 1 - llGetListLength(input); index < 0; ++index) {
list current = llList2List(input, index, index);
if (llListFindList(current, last) < 0) {
last = current;
result += last;
}
}
return result;
}
</source>
</div>
</div>
{{LSLC|Examples|ListUnique}}
{{LSLC|Examples|ListSortedAndUnique}}
[[Category:LSL_User-Defined Functions]]

ListUnique

2025-10-13T20:11:29Z

Lachesis Ethereal: O(n log n) implementation (verified with real world tests)

{{LSL Header}} __NOTOC__

<div id="box">
== Function: [[list]] ListUnique([[list]] {{LSL Param|lAll) }}; ==
<div style="padding: 0.5em;">
Given a list of elements, strips out any duplicates in that list, and returns the de-duped list.

See also: [[List|Lists]]

<source lang="lsl2">
list ListUnique( list lAll ) {
integer i;
list lFiltered = llList2List(lAll, 0, 0);
integer iAll = llGetListLength( lAll );
for (i = 1; i < iAll; ++i) {
if ( llListFindList(lFiltered, llList2List(lAll, i, i) ) == -1 ) {
lFiltered += llList2List(lAll, i, i);
}
}
return lFiltered;
}

</source>

Example:<br />

list mylist = ListUnique(["A", "A", "B", "C", "C", "B"])

would return the list:

["A", "B", "C"]

</div>

Originated in a November 2004 thread led by Chromal Brodsky in the SL Scripting Forum. http://forums-archive.secondlife.com/54/30/28137/1.html

</div>

<div id="box">
== Function: [[list]] ListSortedAndUnique([[list]] {{LSL Param|input}}, [[integer]] {{LSL Param|ascending}}) ==
<div style="padding: 0.5em;">

If you don't need to maintain the order of items (or want them sorted anyway), the following code is consistently about 2x faster on short lists, and 3-5x faster on lists with hundreds of items.

<source lang="lsl2">list ListSortedAndUnique(list input, integer ascending) {
input = llListSort(input, 1, ascending);
integer index;
list last = llList2List(input, 1, 1);
list result = last;
for (index = 1 - llGetListLength(input); index < 0; ++index) {
list current = llList2List(input, index, index);
if (llListFindList(current, last) < 0) {
last = current;
result += last;
}
}
return result;
}
</source>
</div>
</div>
{{LSLC|Examples|ListUnique}}
{{LSLC|Examples|ListSortedAndUnique}}
[[Category:LSL_User-Defined Functions]]