How to inspect array elements based on criteria?

I have a counter file that records page hits - each hit is a UNIX timestamp
in the file. But I'm only interested in page hits in the last 365 days.
The below code creates an array from the file and counts hits based on
interval - day, month or year.

$avs = file($viscounter);
foreach ($avs as $val)
{
if($val>(time()-(86400)))
{
++$v24h;
}
if($val>(time()-(2592000)))
{
++$v30d;
}
if($val>(time()-(31536000)))
{
++$v365d;
}
}
echo $v24h;
echo $v30d;
echo $v365;

The problem is speed - the foreach loop is too slow. This is exacerbated
when the file contains timestamps that are more than one year old - the code
has to loop through additional array elements that I'm not interested in -
sometimes in the tens of thousands. I can't modify the file because it
needs to be kept for historical analysis.

How can I only inspect array elements that are less than or equal to one
year old? Other ways to make this more efficient?

Thanks!

re: How to inspect array elements based on criteria?

deko wrote:[color=blue]
> I have a counter file that records page hits - each hit is a UNIX timestamp
> in the file. But I'm only interested in page hits in the last 365 days.
> The below code creates an array from the file and counts hits based on
> interval - day, month or year.
>
> $avs = file($viscounter);[/color]

/* calculate time offsets once only */
$y = time()-31536000;
$m = time()-2592000;
$d = time()-86400;
[color=blue]
> foreach ($avs as $val)
> {[/color]

/*
[color=blue]
> if($val>(time()-(86400)))
> {
> ++$v24h;
> }
> if($val>(time()-(2592000)))
> {
> ++$v30d;
> }
> if($val>(time()-(31536000)))
> {
> ++$v365d;
> }[/color]

*/

/* reorder your if()s */
if ($val > $y) {
++$v365d;
if ($val > $m) {
++$v30d;
if ($val > $d) ++$v24h;
}
}
[color=blue]
> }
> echo $v24h;
> echo $v30d;
> echo $v365;
>
> The problem is speed - the foreach loop is too slow. This is exacerbated
> when the file contains timestamps that are more than one year old - the code
> has to loop through additional array elements that I'm not interested in -
> sometimes in the tens of thousands. I can't modify the file because it
> needs to be kept for historical analysis.
>
> How can I only inspect array elements that are less than or equal to one
> year old? Other ways to make this more efficient?[/color]

In your original code you are calculating time()-<constant> 3 times for
every line in the file.
You are also comparing every value to three different offsets.

With the changes above you calculate time()-<constant> 3 times.
you compare every value to the year offset and only check for month and
day if it's a value within last year.




If you know for sure the file is ordered, maybe that code can be speeded
up even more by getting rid of most comparisons, but this is just a
guess: try it and use the faster code.

$in_year = false;
$in_month = false;
$in_today = false;

foreach($avs as $val) {
if ($in_year || ($val > $y)) {
++$v365d;
$in_year = true;
if ($in_month || ($val > $m)) {
++$v30d;
$in_month = true;
if ($in_today || ($val > $d)) {
++$v24h;
$in_today = true;
}
}
}
}



--
USENET would be a better place if everybody read: | to email me: use |
http://www.catb.org/~esr/faqs/smart-questions.html | my name in "To:" |
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http://www.expita.com/nomime.html | no attachments. |

re: How to inspect array elements based on criteria?

deko wrote:[color=blue]
> I have a counter file that records page hits - each hit is a UNIX
> timestamp in the file. But I'm only interested in page hits in the
> last 365 days. The below code creates an array from the file and
> counts hits based on interval - day, month or year.
>
> $avs = file($viscounter);
> foreach ($avs as $val)
> {
> if($val>(time()-(86400)))
> {
> ++$v24h;
> }
> if($val>(time()-(2592000)))
> {
> ++$v30d;
> }
> if($val>(time()-(31536000)))
> {
> ++$v365d;
> }
> }
> echo $v24h;
> echo $v30d;
> echo $v365;
>
> The problem is speed - the foreach loop is too slow. This is
> exacerbated when the file contains timestamps that are more than one
> year old - the code has to loop through additional array elements
> that I'm not interested in - sometimes in the tens of thousands. I
> can't modify the file because it needs to be kept for historical
> analysis.
>
> How can I only inspect array elements that are less than or equal to
> one year old? Other ways to make this more efficient?
>
> Thanks![/color]

A minor improvement (without touching the concept, which indead seems to be
a candidate for an efficiency upgrade, I will think about that in the mean
time...) is processing the time() function only once each loop and storing
it in a var.

Then i think you could save some processing by changing the order you check
for year, month, day. But this may be due to the fact the current script
does things you don't want it to do. Looks to me right now a $val that
passes the year test also fulfills the other two tests. If that's what you
want, you could use a case structure and intentionally omit the breaks so
the value falls thru from the first appropriate test. I think the tests take
up most of the time, not the assignments/increments.

I really don't see how your script dismisses all stamps older than 1 year.
It seems to me it does include all these in your counts. But then again,
it's late, had a couple of brewskis and may be wrong...

HTH
Pjotr

re: How to inspect array elements based on criteria?

deko wrote:[color=blue]
> I have a counter file that records page hits - each hit is a UNIX timestamp
> in the file. But I'm only interested in page hits in the last 365 days.
> The below code creates an array from the file and counts hits based on
> interval - day, month or year.
>
> $avs = file($viscounter);
> foreach ($avs as $val)
> {
> if($val>(time()-(86400)))
> {
> ++$v24h;
> }
> if($val>(time()-(2592000)))
> {
> ++$v30d;
> }
> if($val>(time()-(31536000)))
> {
> ++$v365d;
> }
> }
> echo $v24h;
> echo $v30d;
> echo $v365;
>
> The problem is speed - the foreach loop is too slow. This is exacerbated
> when the file contains timestamps that are more than one year old - the code
> has to loop through additional array elements that I'm not interested in -
> sometimes in the tens of thousands. I can't modify the file because it
> needs to be kept for historical analysis.
>
> How can I only inspect array elements that are less than or equal to one
> year old? Other ways to make this more efficient?
>
> Thanks!
>
>[/color]

Deko,

You REALLY need to learn to use a database, there are builtin functions that do
all of this for you and would make your counter be able to store a lot more
data. Currently, what happens when 2 people try to login simultaneously and
write to that log file? Is there contention that will cause a login failure?

Once you have it in a database, then it is easy to do something like (This is
not the exact syntax, you will need to do that yourself -- call it a learning
excercise.

select fielda, fieldb from logtable where datetime > time()-(2592000)

on access to a page you would use an insert statement

insert into logtable values('someuser','somepage',<?php time() ?>);

Now you can not only see how many visitors, but also which page(s) they hit.

I would write it for you, but I am not getting paid to do your job... :)
--
Michael Austin.
Consultant - Available.
Donations welcomed. Http://www.firstdbasource.com/donations.html
:)

re: How to inspect array elements based on criteria?

On Mon, 19 Jul 2004 21:32:17 GMT, "deko" <nospam@hotmail.com> wrote:
[color=blue]
>I have a counter file that records page hits - each hit is a UNIX timestamp
>in the file. But I'm only interested in page hits in the last 365 days.
>The below code creates an array from the file and counts hits based on
>interval - day, month or year.
>
>$avs = file($viscounter);
>foreach ($avs as $val)
>{
> if($val>(time()-(86400)))
> {
> ++$v24h;
> }
> if($val>(time()-(2592000)))
> {
> ++$v30d;
> }
> if($val>(time()-(31536000)))
> {
> ++$v365d;
> }
>}
>echo $v24h;
>echo $v30d;
>echo $v365;
>
>The problem is speed - the foreach loop is too slow. This is exacerbated
>when the file contains timestamps that are more than one year old - the code
>has to loop through additional array elements that I'm not interested in -
>sometimes in the tens of thousands. I can't modify the file because it
>needs to be kept for historical analysis.
>
>How can I only inspect array elements that are less than or equal to one
>year old? Other ways to make this more efficient?[/color]

are you sure it's just the foreach loop that's taking excessive time?
the file read operation will also take a long time for a large file.

anyway, it would speed things up if you didn't make 3 seperate calls
to the time() function and 3 seperate mathematical calculations for
every line of the file... something like this might speed the foreach
loop considerably:

<?php
// read data file
$avs = file($viscounter);
// get current time
$now = time();
// define values for our test times
// (use constants rather than variables for processing speed)
define('TIME24h', $now - 86400);
define('TIME30d', $now - 2592000);
define('TIME365d', $now - 31536000);
// process the data
foreach ($avs as $val)
{
if ($val > TIME24h)
{
++$v24h;
}
if ($val > TIME30d)
{
++$v30d;
}
if ($val > TIME365d)
{
++$v365d;
}
else
{
// entry is older than 365 days, so stop processing
break;
}
}
echo $v24h;
echo $v30d;
echo $v365;
?>

a _much_ better way would be to store your page hits in a database -
you could then also store other info, such as client IP, browser type,
etc.

as long as the timestamp field is indexed, lookups based on that field
will be very fast.

you would then do something like this to get number of hits in the
last 24 hours (in MySQL):

"SELECT COUNT(timestamp) AS hits FROM page_hits WHERE timestamp >
UNIX_TIMESTAMP() - 86400"


hth,
h.c.

re: How to inspect array elements based on criteria?

> You REALLY need to learn to use a database, there are builtin functions
that do all of this

Agreed, but the goal here is to avoid using a database. Actually, it's
working pretty well - except for that bit of inefficient code.
[color=blue]
> call it a learning excercise[/color]

MySql is next week - PHP is this week :)
[color=blue]
> Is there contention that will cause a login failure?[/color]

Yes, there is the possibility for contention, but I make sure there is a
lock on the file before writing, and the code will retry to get the lock if
it cannot the first time.
[color=blue]
> I would write it for you, but I am not getting paid to do your job... :)[/color]

neither am i :)

re: How to inspect array elements based on criteria?

> If you know for sure the file is ordered, maybe that code can be speeded[color=blue]
> up even more by getting rid of most comparisons, but this is just a
> guess: try it and use the faster code.[/color]

Yes, the file is ordered - the oldest time is the first line; the newest
time is the last line.
[color=blue]
> $in_year = false;
> $in_month = false;
> $in_today = false;
>
> foreach($avs as $val) {
> if ($in_year || ($val > $y)) {
> ++$v365d;
> $in_year = true;
> if ($in_month || ($val > $m)) {
> ++$v30d;
> $in_month = true;
> if ($in_today || ($val > $d)) {
> ++$v24h;
> $in_today = true;
> }
> }
> }
> }
>[/color]

This looks great! I will give it a try. Thanks!

re: How to inspect array elements based on criteria?

> are you sure it's just the foreach loop that's taking excessive time?[color=blue]
> the file read operation will also take a long time for a large file.[/color]

Good point - but what do you think is a large file? 100K? 1Mg? 5Mg?
[color=blue]
> anyway, it would speed things up if you didn't make 3 seperate calls
> to the time() function and 3 seperate mathematical calculations for
> every line of the file... something like this might speed the foreach
> loop considerably:
>
> <?php
> // read data file
> $avs = file($viscounter);
> // get current time
> $now = time();
> // define values for our test times
> // (use constants rather than variables for processing speed)[/color]

Great! Will do.
[color=blue]
> define('TIME24h', $now - 86400);
> define('TIME30d', $now - 2592000);
> define('TIME365d', $now - 31536000);
> // process the data
> foreach ($avs as $val)
> {
> if ($val > TIME24h)
> {
> ++$v24h;
> }
> if ($val > TIME30d)
> {
> ++$v30d;
> }
> if ($val > TIME365d)
> {
> ++$v365d;
> }
> else
> {
> // entry is older than 365 days, so stop processing
> break;[/color]

Sounds good - I did not realize I could exit the foreach loop with "break".
I think this may be the best way to deal with entries that are over 1 year
old.
[color=blue]
> }
> }
> echo $v24h;
> echo $v30d;
> echo $v365;
> ?>
>
> a _much_ better way would be to store your page hits in a database -
> you could then also store other info, such as client IP, browser type,
> etc.
>
> as long as the timestamp field is indexed, lookups based on that field
> will be very fast.
>
> you would then do something like this to get number of hits in the
> last 24 hours (in MySQL):
>
> "SELECT COUNT(timestamp) AS hits FROM page_hits WHERE timestamp >
> UNIX_TIMESTAMP() - 86400"[/color]

10-4 on the MySql idea - but there's a reason I am trying to do this with a
file-based script.

Thanks for your help!

re: How to inspect array elements based on criteria?

On Tue, 20 Jul 2004 00:16:48 GMT, "deko" <nospam@hotmail.com> wrote:
[color=blue][color=green]
>> are you sure it's just the foreach loop that's taking excessive time?
>> the file read operation will also take a long time for a large file.[/color]
>
>Good point - but what do you think is a large file? 100K? 1Mg? 5Mg?[/color]

depends on a lot of things - processor speed, disk read speed, other
things happening on the machine, etc.
[color=blue]
>Sounds good - I did not realize I could exit the foreach loop with "break".
>I think this may be the best way to deal with entries that are over 1 year
>old.[/color]

ah.. i've just read another post of yours in this thread in which you
said:
[color=blue]
>Yes, the file is ordered - the oldest time is the first line; the newest
>time is the last line.[/color]

which complicates things... my example would only work if the lines
were in newest-first format...

you _could_ reverse the array once you've read it in from file, but
this would add to script time
(http://www.php.net/manual/en/function.array-reverse.php)

but better to work through the array backwards...

<?php
$avs = file($viscounter);
// do other stuff (set time constants, etc)
for( $i=count($avs)-1; $i>=0; $i-- )
{
if( $avs[$i] > TIME24h )
{
...
}
...
}
?>

re: How to inspect array elements based on criteria?

> but better to work through the array backwards...[color=blue]
>
> <?php
> $avs = file($viscounter);
> // do other stuff (set time constants, etc)
> for( $i=count($avs)-1; $i>=0; $i-- )
> {
> if( $avs[$i] > TIME24h )
> {
> ...
> }
> ...
> }
> ?>[/color]

going to gin this up now... will let you know how it works...

re: How to inspect array elements based on criteria?

> ah.. i've just read another post of yours in this thread in which you[color=blue]
> said:
>[color=green]
> >Yes, the file is ordered - the oldest time is the first line; the newest
> >time is the last line.[/color]
>
> which complicates things... my example would only work if the lines
> were in newest-first format...
>
> you _could_ reverse the array once you've read it in from file, but
> this would add to script time
> (http://www.php.net/manual/en/function.array-reverse.php)
>
> but better to work through the array backwards...
>
> <?php
> $avs = file($viscounter);
> // do other stuff (set time constants, etc)
> for( $i=count($avs)-1; $i>=0; $i-- )
> {
> if( $avs[$i] > TIME24h )
> {
> ...
> }
> ...
> }
> ?>
>[/color]

This seems to work - much faster! Thanks!

define('TIME24h', $now - 86400);
define('TIME30d', $now - 2592000);
define('TIME365d', $now - 31536000);
$avs = file($viscounter);
for( $i=count($avs)-1; $i>=0; $i-- )
{
if( $avs[$i] > TIME24h )
{
++$v24h;
}
if( $avs[$i] > TIME30d )
{
++$v30d;
}
if( $avs[$i] > TIME365d )
{
++$v365d;
}
if( $avs[$i] < TIME365d )
{
echo "<br>some entries are older than 1 year";
break;
//does break statement look okay?
}
}
echo "<br>v24h = ".$v24h;
echo "<br>v30d = ".$v30d;
echo "<br>v365d = ".$v365d;

re: How to inspect array elements based on criteria?

> but better to work through the array backwards...
[color=blue]
> $avs = file($viscounter);
> for( $i=count($avs)-1; $i>=0; $i-- )[/color]

Not sure I understand this...

count($avs) is the line number of the last line in the file - correct?

So if it's a 10-line file, the for statement says:

start with i = 9,
while i is greater than or equal to 0,
decrement i by one.

Why start at 9 rather than 10?
Why start at the bottom of the file? Is that where the pointer is in the
array, after it reads the file into memory? How is it more efficient?

re: How to inspect array elements based on criteria?

I noticed that Message-ID:
<FV0Lc.24185$dv7.11361@newssvr27.news.prodigy.co m> from deko contained
the following:
[color=blue]
>count($avs) is the line number of the last line in the file - correct?[/color]

Nope, it's the number of elements in the array.[color=blue]
>
>So if it's a 10-line file, the for statement says:[/color]
10 element array[color=blue]
>
>start with i = 9,
>while i is greater than or equal to 0,
>decrement i by one.
>
>Why start at 9 rather than 10?[/color]

because arrays start at [0]

--
Geoff Berrow (put thecat out to email)
It's only Usenet, no one dies.
My opinions, not the committee's, mine.
Simple RFDs http://www.ckdog.co.uk/rfdmaker/

re: How to inspect array elements based on criteria?

> >count($avs) is the line number of the last line in the file - correct?[color=blue]
>
> Nope, it's the number of elements in the array.[color=green]
> >
> >So if it's a 10-line file, the for statement says:[/color]
> 10 element array[color=green]
> >
> >start with i = 9,
> >while i is greater than or equal to 0,
> >decrement i by one.
> >
> >Why start at 9 rather than 10?[/color]
>
> because arrays start at [0][/color]

I see. But I'm still curious how it's more efficeint to start at the last
element in the array.
[color=blue]
> for( $i=count($avs)-1; $i>=0; $i-- )[/color]

Is this because that's where the pointer is or something like that - or
should the array be reversed?

re: How to inspect array elements based on criteria?

I noticed that Message-ID:
<bx3Lc.12762$GU.4325@newssvr25.news.prodigy.com> from deko contained the
following:
[color=blue]
>I see. But I'm still curious how it's more efficeint to start at the last
>element in the array.[/color]
Because that is how your file is ordered.

--
Geoff Berrow (put thecat out to email)
It's only Usenet, no one dies.
My opinions, not the committee's, mine.
Simple RFDs http://www.ckdog.co.uk/rfdmaker/

re: How to inspect array elements based on criteria?

> >I see. But I'm still curious how it's more efficeint to start at the
last[color=blue][color=green]
> >element in the array.[/color]
> Because that is how your file is ordered.[/color]

The file is ordered:

oldest
newest

Here is the complete code:

$avs = file($viscounter);
for( $i=count($avs)-1; $i>=0; $i-- )
{
if( $avs[$i] > TIME24h )
{
++$v24h;
}
if( $avs[$i] > TIME30d )
{
++$v30d;
}
if( $avs[$i] > TIME365d )
{
++$v365d;
}
if( $avs[$i] < TIME365d )
{
echo "<br>There are old entries.";
break;
}
}

It's more efficient to start at the last element of the $avs array - which
is the newest entry - because of the way the if statements are sequenced -
is this correct?

Okay, what if I reversed the order of the if statements?
Would I then use this:

$c=count($avs)
for( $i = 0; $i = $c; $i++ )

?

re: How to inspect array elements based on criteria?

"deko" <nospam@hotmail.com> wrote in message
news:jl4Lc.12768$wa1.81@newssvr25.news.prodigy.com ...[color=blue][color=green][color=darkred]
> > >I see. But I'm still curious how it's more efficeint to start at the[/color][/color]
> last[color=green][color=darkred]
> > >element in the array.[/color]
> > Because that is how your file is ordered.[/color]
>
> The file is ordered:
>
> oldest
> newest
>
> Here is the complete code:
>
> $avs = file($viscounter);
> for( $i=count($avs)-1; $i>=0; $i-- )
> {
> if( $avs[$i] > TIME24h )
> {
> ++$v24h;
> }
> if( $avs[$i] > TIME30d )
> {
> ++$v30d;
> }
> if( $avs[$i] > TIME365d )
> {
> ++$v365d;
> }
> if( $avs[$i] < TIME365d )
> {
> echo "<br>There are old entries.";
> break;
> }
> }
>
> It's more efficient to start at the last element of the $avs array - which
> is the newest entry - because of the way the if statements are sequenced -
> is this correct?
>
> Okay, what if I reversed the order of the if statements?
> Would I then use this:
>
> $c=count($avs)
> for( $i = 0; $i = $c; $i++ )
>[/color]

I meant: for( $i = 0; $i < $c; $i++ )

re: How to inspect array elements based on criteria?

deko wrote:[color=blue]
>
> "deko" <nospam@hotmail.com> wrote in message
> news:jl4Lc.12768$wa1.81@newssvr25.news.prodigy.com ...[color=green][color=darkred]
>> > >I see. But I'm still curious how it's more efficeint to start at the[/color]
>> last[color=darkred]
>> > >element in the array.
>> > Because that is how your file is ordered.[/color]
>>
>> The file is ordered:
>>
>> oldest
>> newest
>>
>> Here is the complete code:
>>
>> $avs = file($viscounter);
>> for( $i=count($avs)-1; $i>=0; $i-- )
>> {
>> if( $avs[$i] > TIME24h )
>> {
>> ++$v24h;
>> }
>> if( $avs[$i] > TIME30d )
>> {
>> ++$v30d;
>> }
>> if( $avs[$i] > TIME365d )
>> {
>> ++$v365d;
>> }
>> if( $avs[$i] < TIME365d )
>> {
>> echo "<br>There are old entries.";
>> break;
>> }
>> }
>>
>> It's more efficient to start at the last element of the $avs array - which
>> is the newest entry - because of the way the if statements are sequenced -
>> is this correct?
>>
>> Okay, what if I reversed the order of the if statements?
>> Would I then use this:
>>
>> $c=count($avs)
>> for( $i = 0; $i = $c; $i++ )
>>[/color]
>
> I meant: for( $i = 0; $i < $c; $i++ )[/color]

No.


Let's say you have a file with 1, 2, 3, 4, 5, 6, 7, 8, 9 each on its
line and you want to output the values > 5

if you start at the top [ for($i=0; $i<8; ++$i) ] you do:

compare 1 with 5 -- !>; continue;
compare 2 with 5 -- !>; continue;
compare 3 with 5 -- !>; continue;
compare 4 with 5 -- !>; continue;
compare 5 with 5 -- !>; continue;
compare 6 with 5 -- >; print and continue;
compare 7 with 5 -- >; print and continue;
compare 8 with 5 -- >; print and continue;
compare 9 with 5 -- >; print and continue;


If you start at the bottom [ for($i=8; $i>=0; --$i) ] you do:

compare 9 with 5 -- >; print and continue;
compare 8 with 5 -- >; print and continue;
compare 7 with 5 -- >; print and continue;
compare 6 with 5 -- >; print and continue;
compare 5 with 5 -- !>; break;

This way you will not compare 4, 3, 2, or 1!
If there are a large number of records you want to ignore, savings are
enormous!

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re: How to inspect array elements based on criteria?

> Let's say you have a file with 1, 2, 3, 4, 5, 6, 7, 8, 9 each on its[color=blue]
> line and you want to output the values > 5
>
> if you start at the top [ for($i=0; $i<8; ++$i) ] you do:
>
> compare 1 with 5 -- !>; continue;
> compare 2 with 5 -- !>; continue;
> compare 3 with 5 -- !>; continue;
> compare 4 with 5 -- !>; continue;
> compare 5 with 5 -- !>; continue;
> compare 6 with 5 -- >; print and continue;
> compare 7 with 5 -- >; print and continue;
> compare 8 with 5 -- >; print and continue;
> compare 9 with 5 -- >; print and continue;
>
>
> If you start at the bottom [ for($i=8; $i>=0; --$i) ] you do:
>
> compare 9 with 5 -- >; print and continue;
> compare 8 with 5 -- >; print and continue;
> compare 7 with 5 -- >; print and continue;
> compare 6 with 5 -- >; print and continue;
> compare 5 with 5 -- !>; break;
>
> This way you will not compare 4, 3, 2, or 1!
> If there are a large number of records you want to ignore, savings are
> enormous![/color]

Thanks for the reply. I understand your logic, and it makes sense in your
example. I assume you agree, then, that this:

for( $i=count($avs)-1; $i>=0; $i-- )

is best in my situation.

The oldest entry is at the top of the file (which is read into array $avs),
making $avs[0] the oldest entry - and it is the oldest entries (>1yr old)
that we are not interested in. Therefore, starting at the last array
element (the newest entry) makes sense, as you've illustrated.