Populate an array with strings of words where each element is one word less than the previous

Question

When I run the following code, I'm receiving this output:

PHP
PHP What
PHP What is
PHP What is PHP

However I want to receive the following output:

PHP What is PHP
PHP What is
PHP What
PHP

What thing needs to change to extract values from Upper to Lower

<?php
$stringSentence = 'PHP What is PHP';
$stringSentence = preg_replace('/\s+/', ' ', $stringSentence);
$buffer = '';
$count = 1;
$length = strlen($stringSentence);
for ($i = 0; $i < $length; $i++) {
    if ($stringSentence[$i] !== ' ') {
       $buffer .= $stringSentence[$i];
    } else {
        //echo ' ' . $count++ . ' ' . $buffer . '&lt;/br&gt;';
        $pieces = explode(" ", $stringSentence);
        $first_part = implode(" ", array_splice($pieces, 0, $count++));
        echo '' . $first_part . '</br>';
        $buffer = '';
    }
}

$pieces = explode(" ", $stringSentence);
$first_part = implode(" ", array_splice($pieces, 0, $count++));

echo '' . $first_part . '';

rozsazoltan · Accepted Answer · 2025-09-18 06:52:40Z

0

Here, based on the $words array, I can determine how many words I have in $total. Then, by decreasing $total, I keep slicing the array from index 0 up to the $i element, and join the words together with spaces.

<?php

$stringSentence = 'PHP What is the best way to get the first 5 words of a str?';
$words = explode(" ", $stringSentence);
$total = count($words);

for ($i = $total; $i > 0; $i--) {
    echo implode(" ", array_slice($words, 0, $i)) . PHP_EOL;
}

PHP playground

answered Sep 18 at 6:52

rozsazoltan

18.4k8 gold badges49 silver badges147 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

lukas.j · Accepted Answer · 2025-09-18 14:40:55Z

Another approach would be to extract the positions of all spaces plus the index of the end of the string with the help of regular expressions:

preg_match_all('~ |$~', $string, $indexes, PREG_OFFSET_CAPTURE);

This will fill the third argument $indexes of the preg_match_all call as follows:

Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [0] =>  
                    [1] => 3
                )

            [1] => Array
                (
                    [0] =>  
                    [1] => 8
                )

            [2] => Array
                (
                    [0] =>  
                    [1] => 11
                )

            [3] => Array
                (
                    [0] => 
                    [1] => 15
                )

        )

)

So the positions are in $indexes[0] and they are at index 1 in a subarray, therefore with array_column these values can be extracted, and the result can be reversed with array_reverse:

$indexes = array_reverse(array_column($indexes[0], 1));

Which gives us:

Array
(
    [0] => 15
    [1] => 11
    [2] => 8
    [3] => 3
)

Then with a loop over these index values and the help of substr the parts of the sentence can be extracted:

$result = [];
foreach($indexes as $index) {
  $result[] = substr($string, 0, $index);
}

Or in a functional programming style:

$result = array_map(fn($index) => substr($string, 0, $index), $indexes);

The final array $result will look like this:

Array
(
    [0] => PHP What is PHP
    [1] => PHP What is
    [2] => PHP What
    [3] => PHP
)

mickmackusa · Accepted Answer · 2025-09-29 11:35:50Z

0

I would not try to salvage your coding attempt; I find it too convoluted relative to the simplicity of the task. Basically, you need to use a loop to truncate the input string before its last space and populate an array of those modified strings until there are no more spaces. As soon as there are no more spaces in the input string, preg_replace() will fail to replace anything and the loop will break. In terms of time complexity, it will always perform one function call per word. Demo

$string = "PHP What is PHP"; // assumed to be trimmed already

do {
    $result[] = $string;
    $string = preg_replace('/\s+\S+$/', '', $string, 1, $count);
} while ($count);

var_export($result);

answered Sep 29 at 11:35

mickmackusa♦

49.2k13 gold badges98 silver badges165 bronze badges

Collectives™ on Stack Overflow

Populate an array with strings of words where each element is one word less than the previous

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related