<?php

    $str ="iamtheone";
    
    // Calculate the frequency table for all letters
    $letters = array_fill_keys(range('a', 'z'), ' ');
    $freq_count = array_merge(
        $letters,
        array_count_values(str_split(strtolower($str)))
    );
     
    // Plot the display chart
    for ($line = max($freq_count); $line > 0; --$line) {
        echo implode(
            ' ', 
            array_map(
                function ($value) use ($line) {
                    return ($value >= $line) ? '*' : ' ';
                },
                $freq_count
            )
        );
        echo PHP_EOL;
    }
    echo implode(' ', array_keys($freq_count)), PHP_EOL;