How to best add element to array at arbitrary index in PHP? - php

Question

How can I write a solution for which the current PHP interpreter (5.4) is smart enough to simply do about 3-5 copies instead of a full on item-by-item array sort?
Note, I know a few methods to insert an element into an indexed array. However this does not satisfy my understanding. For instance in C++, you can do something using std::copy or make a struct or union as a multi-element array cursor.
So I wonder if I play by PHP's rules somehow, what syntax can one use to have, under the hood, something closer to
Copy the [range of elements from some index to the end of A] into temp C
Copy B into A[Index],
Copy C into A[Index+count(B)]
Than this...
$MasterItemList = $Page[$CurrentPage]->GetItems(); /* Returns an array with 512 Items. */
$UpdateList = GetUpdatePage(); /* Returns multi-dimensional array such that:
$result[][0]=an index and
$result[][1]=a list of items */
foreach($UpdateList as $Update)
{ foreach($Update as $cursor => $ItemList)
{
$cursor=$cursor+0; //to int..
$numitems=count($ItemList);
if($ItemList[0]->NewAddition)
{
$BeforeUpdate=array_splice($MasterItemList,0, $cursor, true);
$AfterUpdate=array_splice($MasterItemList, $cursor+$numitems, 0);
$MasterItemList=array_merge($BeforeUpdate,$ItemList,$AfterUpdate);
$Page[$CurrentPage]->OffsetCorrection+=$numitems;
}
else
{
$i=0;
foreach($ItemList as $LineItem)
{
$MasterItemList[$cursor+$i] = $LineItem;
$i++;
}
}
}
}
Forgive me if I've a few errors jotting this down, let me know and I'll correct them.
Namely though, I dont think proper referencing and scope are available to the interpreter for it to be able to do the logic directly using this method. It's already a woefully expensive looking thing.. What can be done to do this 'the right way' for PHP?
Examples:
// An Update List
Array(
[0] => Array(
[0] => 31
[1] => Array(
[1] => stdClass Object
(
[NewAddition] => false
[Name] => "********"
[Date] => 1364920943
[Active] => 1
.
.
.
)
[2] => stdClass Object
(
[NewAddition] => false
[Name] => "********"
[Date] => 1364920943
[Active] => 1
.
.
.
)
[3] => stdClass Object
(
[NewAddition] => false
[Name] => "********"
[Date] => 1364920943
[Active] => 1
.
.
.
)
)
)
)
And MasterItemList is simply an array of these same objects (class Item).
A few things to note:
This data is only accessed in a purely sequential manner anywhere it would matter for this script.
Only the first item in a newly inserted set needs to be checked for update in this part of the script. All items following in the set will be always be new.
Items trailing over 512 are auto-adjusted into the next page load. I can adjust size of pages to trade between array sorting performance & data fetch performance (async buffered).

Answer 1

First of all, PHP arrays are not "arrays" in the data structure sense; they are actually hash tables and doubly linked lists rolled into one. When you are indexing into an array e.g. with $list[$i] $i is hashed to find the corresponding element; it's not simple arithmetic as it is in e.g. C++.
Additionally, since arrays are also linked lists the implementation of array_splice is much more efficient than it might appear, at least if the portion being removed is small enough (hashing the new items is normally fast, and interposing items at a certain place of a linked list is constant time).
Of course this means that PHP arrays consume much more memory than a "pure" array would and they are also slower if all you are intending is index-based access. In those situations the SPL offers SplFixedArray which is an implementation of an array in the data structure sense of the word.
In your particular case, array_splice should be your first option; you can insert an array chunk with just one call:
array_splice($MasterItemList, $cursor, 0, $ItemList);