Concordance table

ConcordanceTable.php

<?php

CONST TEXT = 'Given an arbitrary text document written in English, write a program that will generate a concordance, i.e. an alphabetical list of all word occurrences, labeled with word frequencies. Bonus: label each word with the sentence numbers in which each occurrence appeared.';

//Build concordance table
function build_table($text)
{
    $table = [];
    $text = format_text($text);
    
    // Split sentences on regex so as to cover acronym edge case
    $sentences = preg_split('/(?<![i\.e\.])\./', $text);

    foreach ($sentences as $i => $sentence)
    {
        $words = explode(' ', $sentence);
        foreach ($words as $j => $word)
        {
            $table = update_count($table, $word);
            $table = update_sentence($table, $word, $i);
        }
    }

    return $table;
}

function format_text($text)
{
    $text = strtolower($text);
    $text = str_replace(',', '', $text);
    return $text;
}

// Add word to table and update the number
// of times it has appeared
function update_count($table, $word)
{
    // If the word is in the table, increment count
    if (isset($table[$word][0]))
    {
        $table[$word][0]++;
    }
    // Add word to table with count 1
    else
    {
        $table[$word][0] = 1;
    }
    return $table;
}

// Mark sentence number where word was found
function update_sentence($table, $word, $i)
{
    $table[$word][1][] = $i+1;
    return $table;
}

// Format table data for printing to console
function format_table($table)
{
    // Add colon to word count, flatten sentence count array deliminate with commas
    foreach ($table as &$table_entry)
    {
        $table_entry = $table_entry[0] . ':' . implode(',', $table_entry[1]);
    }

    // Sort table alphabetically
    ksort($table);
    // Remove match char
    array_shift($table);
    return json_encode($table);
}

$table = build_table(TEXT);
$table = format_table($table);
echo($table);