Simple Pagination with modulus

[nathanj]

I am in the process of trying to learn the concept of modulus and I have been told that I can use it in the process of pagination. Anyone care to explain?

I have a very simple array and I want to put 2 results per page. (this oviously is just to get the process in my head)

<?php

error_reporting(E_ALL);

$animals = array("cat", "dog", "rat", "rabbit", "lion", "tiger", "mouse", "monkey", "fish", "fox");

foreach ($animals as $animals_num => $animal) {

//what to do here?

};

?>

[swdev]

modulus is the 'number left over' when b is divided by a

try this little code snippet to see what I mean

 $num_per_page = 3;
 $max_items = 10;
 for ($i = 0; $i < $max_items; $i++)
 {
   echo $i .' mod ' . $num_per_page . ' = ' . $i % $num_per_page . '<br />'; 
 } 

$num_per_page is the number of items you want on a page.

[nathanj]

I'll give this a try and worry about displaying page links later.

[nathanj]

I don't understand how I can show only 3 animals per page with this?

[nathanj]

<?php

error_reporting(E_ALL);

$animals = array("cat", "dog", "rat", "rabbit", "lion", "tiger", "mouse", "monkey", "fish", "fox");

$num_per_page = 3;

$p = $_GET['p'];

for ($i = 0; $i < count($animals); $i++) {

    if ($i % $num_per_page == $p) {
    
    echo $animals[$i];
    
    };
    
};

?>

I am getting some useful output now I think.

[nathanj]

Another problem is that they won't be in key order as the array is...? This becomes a problem because I want to later apply this to a array which is in order..

[swdev]

Ok - here is a complete example that

1) displays the reqested data
2) builds the links

  $animals = array("cat", "dog", "rat", "rabbit", "lion", "tiger", "mouse", "monkey", "fish", "fox");
  $num_per_page = 3;
  $max_items = 10;
  $total_items = count($animals);
  
  // read passed in page number and validate it
  if (true === isset($_GET['page']))
  {
   $start = intval($_GET['page']);
   if ( ($start < 0) || ($total_items < $start) )
   {
    $start = 0;
   }
  }
  else
  {
   $start = 0;
  }
  
  // calcualte start and end ponits in array
  $start *= $num_per_page;
  $end = $start + $num_per_page;
  if ($total_items < $end)
  {
    $end = $total_items;
  }
  
  // Display the data
  for ($i = $start; $i < $end; $i++)
  {
    echo 'Animal at offset ' . $i . ' is ' . $animals[$i] . '<br />';
  }
  
  // build links
  $link_start = '<a href="' . $_SERVER['PHP_SELF'] . '?page=';
  $link_end = '</a>';
  
  $num_pages = ceil($total_items / $num_per_page);
  for ($i = 0; $i < $num_pages; $i++)
  {
   echo $link_start . $i . '">Page ' . $i . $link_end . '&nbsp;';
  } 

Hopefully there are enough comments for you to modify as required.
Also, I have tried to make it so that it checks for an invalid page number being passed.

[nathanj]

<?php

$animals = array("cat", "dog", "rat", "rabbit", "lion", "tiger", "mouse", "monkey", "fish", "fox");

$num_per_page = 3;

$p = $_GET['p'];

if ( empty($p) || $p < 0 ) {

    $p = 0;
    
};

for ($i = $p * $num_per_page; $i < ($p+1) * $num_per_page; $i++) {

    echo $animals[$i] . "<br />";
    
} 

echo '<a href="' . $_SERVER['PHP_SELF'] . '?p=' . ($p+1) . '">next page</a>'; 

?>

[swdev]

Your code does work, however

1) Once you have viewed a page, there is no way to go back to it, or any previous page

2) You can view past the number of items in the $animals array - not recommended

[nathanj]

I'll muck around with it later. Thanks for your help. My head hurts. ~

[nathanj]

Can you please explain your code indepth so I can learn something from it?

[nathanj]

<?php

error_reporting(E_ALL);

// put file contents into array
$contents = array_reverse(file('quotedb'));

// number of data entries to be displayed
$num_per_page = 20;

// total entries
$total_items = count($contents);

//
if (isset($_GET['p'])) {
    $start = intval($_GET['p']);
    if (($start < 0) || ($total_items < $start)) {
        $start = 0;
    }
} else {
    $start = 0;
}

// calcualte start and end ponits in array
$start *= $num_per_page;
$end = $start + $num_per_page;

if ($total_items < $end) {
    $end = $total_items;
}

// display the data
for ($i = $start; $i < $end; $i++) {
    $line = $contents[$i];
    $explode = explode('#0', $line);
    $date = explode('-', $explode[3]);
    echo '<b>' . $explode[0] . '</b><br />' . $explode[1] . '<br/><i>added by ' . $explode[2] . ' on the ' . date('l \t\h\e jS \o\f F, Y', mktime(0,0,0,$date[1],$date[0],$date[2])) . '</i><br /><br />';
}

// build links
$num_pages = ceil($total_items / $num_per_page);

for ($i = 0; $i < $num_pages; $i++) {
    echo '<a href="' . $_SERVER['PHP_SELF'] . '?page=' . $i . '">Page ' . $i . '</a>&nbsp;|&nbsp;';
}

?>

My edited code.

[swdev]

Certainly - here goes

   $animals = array("cat", "dog", "rat", "rabbit", "lion", "tiger", "mouse", "monkey", "fish", "fox"); 

This is the complete list of items (things) that you want to display, page by page

  $num_per_page = 3;
  $max_items = 10;
  $total_items = count($animals); 

oops, remove the $max_items variable - it is not required.
$num_per_page - this is the number of items to be displayed on a single page.
$total_items - this is the total number of items to be displayed.

   // read passed in page number and validate it
    if (true === isset($_GET['page']))
    {
     $start = intval($_GET['page']);
     if ( ($start < 0) || ($total_items < $start) )
     {
      $start = 0;
     }
    }
    else
    {
     $start = 0;
    } 

Ths section of code is used to retrieve the page number from the link ($_GET['page']) which is then stored in $start.
$start is then checked to make sure that is is between the first and last item in the array. Why? becase you don't want to display non-existent items.

    // calcualte start and end ponits in array
    $start *= $num_per_page;
    $end = $start + $num_per_page;
    if ($total_items < $end)
    {
      $end = $total_items;
    } 

This section of code calculates the start position in the array i.e the first item that you want to display on the selcted page, and also the last item to be displayed, so that you don;t display non-existent items.

    // Display the data
    for ($i = $start; $i < $end; $i++)
    {
      echo 'Animal at offset ' . $i . ' is ' . $animals[$i] . '<br />';
    } 

This section of code actually displays the data, 1 items per line.

    // build links
    $link_start = '<a href="' . $_SERVER['PHP_SELF'] . '?page=';
    $link_end = '</a>'; 

This section of code just creates some variables to be used when generating the links

  $num_pages = ceil($total_items / $num_per_page); 

Calculate the total number of pages to generate links for. ceil returns the next highest valus of the passed in variable, roundng up where necessary

    for ($i = 0; $i < $num_pages; $i++)
    {
     echo $link_start . $i . '">Page ' . $i . $link_end . '&nbsp;';
    } 

This section of codes generates and displays the page links

So
Page 0 displays animals 0 to 2
Page 1 displays animals 3 to 5
Page 2 displays animals 6 to 8
Page 3 displays animals 9 to 10

I hope this explains things in more detail.

Run this code and then do a 'Vie Source' to see what the links look like.

Don't hesitate to ask more questions if I have glossed over anything.

[nathanj]

That is great, the main thing I didn't get was the start and finish variables but I get it now! Thanks mate. Code is working @ http://www.passivekid.com/~nathan/quotebot/quotedb.php

[swdev]

No problems.

Glad it is now working.

One thing, rather than have pages go from 0 to 6, I think it looks better if they go from 1 to 7.

This is easily achieved by modding this one little bit of code

Original code

 for ($i = 0; $i < $num_pages; $i++)
 {
  echo $link_start . $i . '">Page ' . $i . $link_end . '&nbsp;';
 } 

New code

 for ($i = 0; $i < $num_pages; $i++)
 {
  echo $link_start . $i . '">Page ' . ($i + 1) . $link_end . '&nbsp;';
 } 

[nathanj]

Hehe yeah. Thanks.