how to show random articles - php

Question

I am working on project which shows articles and this was done by article manager (a ready to use php script) but I have a problem, I want to show only four article titles and summaries from old list of article randomly which contains 10 article. Any idea how to achieve this process?
I have auto generated summary of article
<div class="a1">
<h3><a href={article_url}>{subject}</h3>
<p>{summary}<p></a>
</div>
When a new article is added the above code will generated and add into summary page. I want to add it to side of the main article page, where user can see only four article out of ten or more randomly.
<?php
$lines = file_get_contents('article_summary.html');
$input = array($lines);
$rand_keys = array_rand($input, 4);
echo $input[$rand_keys[0]] . "<br/>";
echo $input[$rand_keys[1]] . "<br/>";
echo $input[$rand_keys[2]] . "<br/>";
echo $input[$rand_keys[3]] . "<br/>";
?>
Thanks for your kindness.

Answer 1

Assuming I understood you correctly - a simple solution.
<?php
// Settings.
$articleSummariesLines = file('article_summary.html', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
$showSummaries = 4;
// Check if given file is valid.
$validFile = ((count($articleSummariesLines) % 4 == 0) ? true : false);
if(!$validFile) {
die('Invalid file...');
}
// Count articles and check wether all those articles exist.
$countArticleSummaries = count($articleSummariesLines) / 4;
if($showSummaries > $countArticleSummaries) {
die('Can not display '. $showSummaries .' summaries. Only '. $countArticleSummaries .' available.');
}
// Generate random article indices.
$articleIndices = array();
while(true) {
if(count($articleIndices) < $showSummaries) {
$random = mt_rand(0, $countArticleSummaries - 1);
if(!in_array($random, $articleIndices)) {
$articleIndices[] = $random;
}
} else {
break;
}
}
// Display items.
for($i = 0; $i < $showSummaries; ++$i) {
$currentArticleId = $articleIndices[$i];
$content = '';
for($j = 0; $j < 4; ++$j) {
$content .= $articleSummariesLines[$currentArticleId * 4 + $j];
}
echo($content);
}