Iterate from middle of array

[ChronoFish]

Hi there,

I want to iterate through an array starting at a known index. However the indexes are not linear.

For example I have an array of events keyed by timestamp.

$eventList = array (1064263264 => "event1", 10642635555 => "event2", 1064266666 => "event3", 1064267782 => "event4", 1064268812 =>
"event5");

I basically want to do a "for" or "foreach" but I don't necessarily want to start at key 1064263264 (event1).

I'm looking for something Like

$startEvent = 10642635555;
$endEvent = 1064267782;
for ($event = $startEvent; $event < $lastEvent; $event = nextKey())
{
print $eventList[$event];
}

To make it worse, I can't use a foreach and simply "if" my way out of it because I am already iterating over the entire list and I
would like to avoid a O(x^2) algorithm.

foreach ($eventList as $currentEvent)
{
..... // processing
$startEvent = 10642635555;
$endEvent = 1064267782;
for ($event = $startEvent; $event < $lastEvent; $event = nextKey())
{
print $eventList[$event];
}
..... // more processing
}

Of course there is no "nextKey()" and before rolling my own I thought I would ask if PHP already has a solution for this that I've
missed.

Thanks!
CF

[Pedro Graca]

Re: Iterate from middle of array

ChronoFish wrote (in loooooooooooooo ooooooooooooooo oooong lines):[color=blue]
> I want to iterate through an array starting at a known index.
> However the indexes are not linear.[/color]
[color=blue]
> To make it worse, I can't use a foreach and simply "if" my way out
> of it because I am already iterating over the entire list and I
> would like to avoid a O(x^2) algorithm.
>[/color]
# foreach ($eventList as $currentEvent)
# {


// also use the index inside your loop
foreach ($eventList as $k=>$currentEve nt)
{

[color=blue]
> .... // processing
> $startEvent = 10642635555;
> $endEvent = 1064267782;[/color]

// move the $startEvent and $endEvent outside the loop,
// unless, of course, they are changing inside :)


# for ($event = $startEvent; $event < $lastEvent; $event = nextKey())
# {

// use the $k thing
if ($startEvent <= $k && $k <= $endEvent) print $currentEvent;


# print $eventList[$event];
# }[color=blue]
> .... // more processing
> }[/color]


This way you only go through the array once.
I really didn't understand if you wanted multiple prints of each event
between $startEvent and $endEvent; if you do, this wil not work.
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[Justin Koivisto]

Re: Iterate from middle of array

ChronoFish wrote:[color=blue]
> I want to iterate through an array starting at a known index. However the indexes are not linear.
>
> For example I have an array of events keyed by timestamp.
>
> $eventList = array (1064263264 => "event1", 10642635555 => "event2", 1064266666 => "event3", 1064267782 => "event4", 1064268812 =>
> "event5");
>
> I basically want to do a "for" or "foreach" but I don't necessarily want to start at key 1064263264 (event1).
>
> I'm looking for something Like
>
> $startEvent = 10642635555;
> $endEvent = 1064267782;
> for ($event = $startEvent; $event < $lastEvent; $event = nextKey())
> {
> print $eventList[$event];
> }
>
> To make it worse, I can't use a foreach and simply "if" my way out of it because I am already iterating over the entire list and I
> would like to avoid a O(x^2) algorithm.
>
> foreach ($eventList as $currentEvent)
> {
> .... // processing
> $startEvent = 10642635555;
> $endEvent = 1064267782;
> for ($event = $startEvent; $event < $lastEvent; $event = nextKey())
> {
> print $eventList[$event];
> }
> .... // more processing
> }
>
> Of course there is no "nextKey()" and before rolling my own I thought I would ask if PHP already has a solution for this that I've
> missed.[/color]

Here's my first thought...

$tmp=$eventList ; // ksort doesn't make a copy of the passed array,
ksort($tmp); // it modifies it - need to copy if you want the
// original for use later

foreach($tmp as $k=>$event){
if($k<$startEve nt) continue; // not at the start yet
else if($k>$endEvent ) break; // last one has been done
else echo $event; // print it out
}
unset($tmp);

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PHP POSTERS: Please use comp.lang.php for PHP related questions,
alt.php* groups are not recommended.
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[ChronoFish]

Re: Iterate from middle of array


"Pedro Graca" <hexkid@hotpop. com> wrote in message news:c22dpo$1p4 bac$1@ID-
.....[color=blue]
> This way you only go through the array once.
> I really didn't understand if you wanted multiple prints of each event
> between $startEvent and $endEvent; if you do, this wil not work.[/color]


Thanks so much Pedro. I don't think I stated my intentions strong enough. I do need to go through multiple times as startEvent and
endEvent change on each iteration. I endedup just biteing the bullet and iterate twice through.

I think what I was after was the opposite of the pos() function. It gives you the current key. What I want to do is to be able to
set the "current" position of the array position pointer.

Thanks anyway!

CF

[ChronoFish]

Re: Iterate from middle of array


"Justin Koivisto" <spam@koivi.com > wrote in message news:%H31c.431$ 6c5.16535@news7 .onvoy.net...
[color=blue]
> $tmp=$eventList ; // ksort doesn't make a copy of the passed array,
> ksort($tmp); // it modifies it - need to copy if you want the
> // original for use later
>
> foreach($tmp as $k=>$event){
> if($k<$startEve nt) continue; // not at the start yet
> else if($k>$endEvent ) break; // last one has been done
> else echo $event; // print it out
> }
> unset($tmp);
>[/color]

Hi Justin, Thanks for your help. This is what I was trying to avoid as this gives me 0(n^2) (for every element I iterate through
ever element). As noted in my other response what I was looking for was the opposite of the pos() function. pos() returns the
current key of the arrays internal position pointer. I want to be able to to set it like pos($currentEve nt) and continue iterating
from there. Oh well....

Thanks again,
CF

[Chung Leong]

Re: Iterate from middle of array

Try this:

$indices = array_keys($eve ntList);
$start = array_search($i ndices, $startEvent);
$end = array_search($i ndices, $endEvent);
$range = array_slice($ev entList, $start, $end - $start + 1);

or this

$positions = array_flip(arra y_keys($eventLi st));
$start = $positions[$startEvent];
$end = $positions[$endEvent];
$range = array_slice($ev entList, $start, $end - $start + 1);

$range will be the elements you're interested in.

Uzytkownik "ChronoFish " <deja@chronofis h.com> napisal w wiadomosci
news:bs21c.8082 $oP.2717@lakere ad03...[color=blue]
> Hi there,
>
> I want to iterate through an array starting at a known index. However the[/color]
indexes are not linear.[color=blue]
>
> For example I have an array of events keyed by timestamp.
>
> $eventList = array (1064263264 => "event1", 10642635555 => "event2",[/color]
1064266666 => "event3", 1064267782 => "event4", 1064268812 =>[color=blue]
> "event5");
>
> I basically want to do a "for" or "foreach" but I don't necessarily want[/color]
to start at key 1064263264 (event1).[color=blue]
>
> I'm looking for something Like
>
> $startEvent = 10642635555;
> $endEvent = 1064267782;
> for ($event = $startEvent; $event < $lastEvent; $event = nextKey())
> {
> print $eventList[$event];
> }
>
> To make it worse, I can't use a foreach and simply "if" my way out of it[/color]
because I am already iterating over the entire list and I[color=blue]
> would like to avoid a O(x^2) algorithm.
>
> foreach ($eventList as $currentEvent)
> {
> .... // processing
> $startEvent = 10642635555;
> $endEvent = 1064267782;
> for ($event = $startEvent; $event < $lastEvent; $event = nextKey())
> {
> print $eventList[$event];
> }
> .... // more processing
> }
>
> Of course there is no "nextKey()" and before rolling my own I thought I[/color]
would ask if PHP already has a solution for this that I've[color=blue]
> missed.
>
> Thanks!
> CF
>
>
>[/color]

[ChronoFish]

Re: Iterate from middle of array

"Chung Leong" <chernyshevsky@ hotmail.com> wrote in message news:<DPCdnZnuZ dopE9vd4p2dnA@c omcast.com>...[color=blue]
> Try this:
>
> $indices = array_keys($eve ntList);
> $start = array_search($i ndices, $startEvent);
> $end = array_search($i ndices, $endEvent);
> $range = array_slice($ev entList, $start, $end - $start + 1);
>[/color]

Great idea. I had not considered slice and I think this will work
fine. Not sure what it means in terms of "Big O" but it looks clean.

Thanks!
CF