how to save/restore current array position?

[Magnus Warker]

Hi,

I want to traverse an (associative) array, starting from its current
position, until a certain element is reached. Then, in certain cases, I
want to be able to reset the current position of the array to the one that
we had before touching the array.

I. e., i need something like funcctions getpos and setpos:

----------

$pos = getpos ($list);

do
{
$item = current ($list);
$name = key ($list);

next ($list);
} while (!isWanted ($item));

setpos ($list,$pos);

----------

What I really need in the above example is:
Check, if we *could* get another wanted item from the list, but actually
leave the list (its current position) untouched.

Any ideas?

Many thanks,
Markus

[Shelly]

Re: how to save/restore current array position?


"Magnus Warker" <wagner@abwesen d.de> wrote in message
news:dc05i8$3bj $04$1@news.t-online.com...[color=blue]
> Hi,
>
> I want to traverse an (associative) array, starting from its current
> position, until a certain element is reached. Then, in certain cases, I
> want to be able to reset the current position of the array to the one that
> we had before touching the array.
>
> I. e., i need something like funcctions getpos and setpos:
>
> ----------
>
> $pos = getpos ($list);
>
> do
> {
> $item = current ($list);
> $name = key ($list);
>
> next ($list);
> } while (!isWanted ($item));
>
> setpos ($list,$pos);
>
> ----------
>
> What I really need in the above example is:
> Check, if we *could* get another wanted item from the list, but actually
> leave the list (its current position) untouched.
>
> Any ideas?
>
> Many thanks,
> Markus
>[/color]

Reverse the while and do so that it is a pre-test? As for the setpos and
getpos, there are many ways.

C style:
(1) Set a session variable with the value and read the value.
(2) Pass the variable to the next page and use $_GET

OO style:
encapsulate in the class as a variable in the class. The obect then has
the value of "pos", and getpos and setpos are merely accessor and mutator
methods of the class.

I hope that helps.

Shelly

[Magnus Warker]

Re: how to save/restore current array position?

Hi Shelly,

thank you very much!
[color=blue]
> C style:
> (1) Set a session variable with the value and read the value.
> (2) Pass the variable to the next page and use $_GET[/color]

Which variable are you talking about? There is no "next page". The problem
code is executed at once.
[color=blue]
> OO style:
> encapsulate in the class as a variable in the class. The obect then has
> the value of "pos", and getpos and setpos are merely accessor and mutator
> methods of the class.[/color]

I think I cannot follow. Even when encapsulating the array in an additional
class, the original problem still remains.

What I already tried is to just do the while on a copy of the array, but
copying resets the position.

Thanks,
Magnus

[Shelly]

Re: how to save/restore current array position?


"Magnus Warker" <wagner@abwesen d.de> wrote in message
news:dc09ge$j4l $00$1@news.t-online.com...[color=blue]
> Hi Shelly,
>
> thank you very much!
>[color=green]
>> C style:
>> (1) Set a session variable with the value and read the value.
>> (2) Pass the variable to the next page and use $_GET[/color]
>
> Which variable are you talking about? There is no "next page". The problem
> code is executed at once.[/color]

OK, that is simpler. Here is a suggestion. Set a hidden variable as
"the_index" with a value equal to zero. Then as your index changes, set the
value of the_index to that value. Now you begin the loop at the value of
the_index with a pre-test.

$pos = $POST['the_index'] or $pos = $the_index. (I'm not sure which)
while (blah) do {
}
[color=blue]
>[color=green]
>> OO style:
>> encapsulate in the class as a variable in the class. The obect then
>> has
>> the value of "pos", and getpos and setpos are merely accessor and mutator
>> methods of the class.[/color]
>
> I think I cannot follow. Even when encapsulating the array in an
> additional
> class, the original problem still remains.
>
> What I already tried is to just do the while on a copy of the array, but
> copying resets the position.[/color]

class theDef {
var pos;
}

$theObj = new theObj();
$i = $theObj->getpos();

while (blah) do {
stuff
$i++;
theObj->setpos($i);
}


Shelly

[Magnus Warker]

Re: how to save/restore current array position?

Dear Shelly,

thank you again for giving hints! .-)
[color=blue]
> OK, that is simpler. Here is a suggestion. Set a hidden variable as
> "the_index" with a value equal to zero. Then as your index changes, set
> the
> value of the_index to that value. Now you begin the loop at the value of
> the_index with a pre-test.
>
> $pos = $POST['the_index'] or $pos = $the_index. (I'm not sure which)
> while (blah) do {
> }[/color]

I think there is a misunderstandin g here:

I have an associative array, and my understanding of this kind of creature
is that we cannot access elements by a numerical index, right?

So storing a value in $POST['the_index'] means storing the key of the
current item.

In analogy, retrieving a value from $POST['the_index'] means retrieving the
key of the item which was the current item some time ago.

However, having the key of the item which was the current item some time ago
does not enable me to set the internal pointer of the "current" item within
the array, does it?

My problem is not storing and retrieving some values, but modifying the
internal state of an array.

See what I mean?

Magnus

[Shelly]

Re: how to save/restore current array position?


"Magnus Warker" <wagner@abwesen d.de> wrote in message
news:dc0cu5$nap $03$1@news.t-online.com...[color=blue]
> Dear Shelly,
>
> thank you again for giving hints! .-)[/color]

You are welcome. I was at your stage in PHP just a short while ago.
[color=blue][color=green]
>> OK, that is simpler. Here is a suggestion. Set a hidden variable as
>> "the_index" with a value equal to zero. Then as your index changes, set
>> the
>> value of the_index to that value. Now you begin the loop at the value of
>> the_index with a pre-test.
>>
>> $pos = $POST['the_index'] or $pos = $the_index. (I'm not sure
>> which)
>> while (blah) do {
>> }[/color]
>
> I think there is a misunderstandin g here:
>
> I have an associative array, and my understanding of this kind of creature
> is that we cannot access elements by a numerical index, right?[/color]

Not as far as I know.
[color=blue]
> So storing a value in $POST['the_index'] means storing the key of the
> current item.[/color]

You get the value of a variable in $_POST.
[color=blue]
> In analogy, retrieving a value from $POST['the_index'] means retrieving
> the
> key of the item which was the current item some time ago.[/color]

??? $_POST gets the value of a field on the form..... and it is $_POST, not
$POST.
[color=blue]
> However, having the key of the item which was the current item some time
> ago
> does not enable me to set the internal pointer of the "current" item
> within
> the array, does it?[/color]

I guess. Your language is confusing me.
[color=blue]
> My problem is not storing and retrieving some values, but modifying the
> internal state of an array.
>
> See what I mean?[/color]

No. What do you mean by "modifying the internal state of an array."?
Changing values in the array? Dropping items from the array by unset() ing
them? What **do** you mean?

Shelly
[color=blue]
>
> Magnus[/color]

[Magnus Warker]

Re: how to save/restore current array position?

Dear Shelly!
[color=blue]
> You are welcome. I was at your stage in PHP just a short while ago.[/color]
[color=blue][color=green]
>> See what I mean?[/color][/color]
[color=blue]
> No. What do you mean by "modifying the internal state of an array."?
> Changing values in the array? Dropping items from the array by unset()
> ing
> them? What **do** you mean?[/color]

If you don't understand the problem, you should take a look at the array
functions 'current', 'reset' and 'next'. They all change the internal
position of an array.

Nevertheless, thanks for replying to my question,
Magnus

[Steve]

Re: how to save/restore current array position?

[color=blue]
> I want to traverse an (associative) array, starting from its current
> position, until a certain element is reached. Then, in certain cases, I
> want to be able to reset the current position of the array to the one that
> we had before touching the array.[/color]

Even associative arrays have internal numeric keys which (a) are used
by prev(), next() to order the retrieval and (b) can be used to set the
current array pointer randomly.

array_keys() creates an array of the internal numeric keys that can be
used to navigate the array instead of using prev(), next() etc. That
way you have complete control over which element to access next.


$test = array();

$test[] = 'One';
$test[] = 'Two';
$test[] = 'Three';
$test[] = 'Four';
$test[] = 'Five';
$test[] = 'Six';

$keys = array_keys( $test );

$ptr = reset( $keys );
print $test[ $ptr ] . "\n";

$ptr = next( $keys );
print $test[ $ptr ] . "\n";

$ptr = next( $keys );
print $test[ $ptr ] . "\n";

print "remembering... \n";

$remember = $ptr;

$ptr = next( $keys );
print $test[ $ptr ] . "\n";

$ptr = next( $keys );
print $test[ $ptr ] . "\n";

print "recalling...\n ";

$ptr = $remember;

reset( $keys );
while( $ptr < next( $keys ) );

$ptr = next( $keys );
print $test[ $ptr ] . "\n";

$ptr = next( $keys );
print $test[ $ptr ] . "\n";


// output...

One
Two
Three
remembering...
Four
Five
recalling...
Three
Four



---
Steve