Convert consecutive comma-separated days into hyphenated day ranges

Question

I am trying to compact an expression of individual days into a shorter expression including hyphen-separate ranges.

Examples:

• mon,tue,wed,thu,fri,sat
  to be:
  mon-sat
• mon,tue,wed,fri,sat
  to be
  mon-wed,fri-sat

My coding attempt:

function dayrange($days){
    $days = explode(",", str_replace(" ","",$days));
    return reset($days) . "-" . end($days);
}

How can I shorten the multi-day expression so that consecutive days are merged into a range of days?

Answer 1

Basically, I would approach this by:

1. Converting the days to corresponding numeric values
2. Turning the array of numbers into a string with ranges
3. Converting the numbers in the string back into days of the week

I wrote some code to do that:

/**
 * Convert an array of numbers to a string containing ranges and single values
 * @param array $numbers an array of numbers
 * @return string
 */
function compressNumbers($numbers) {
    $result = array();
    sort($numbers);
    $previousValue = reset($numbers);
    $startValue = $previousValue;
    foreach ($numbers as $value) {
        if ($value > $previousValue + 1) {
            if ($startValue == $previousValue) {
                $result[] = $startValue;
            } else {        
                $result[] = $startValue . '-' . $previousValue;
            }
            $startValue = $value;
        }
        $previousValue = $value;
    }
    if ($startValue == $previousValue) {
        $result[] = $startValue;
    } else {        
        $result[] = $startValue . '-' . $previousValue;
    }
    return implode(',', $result);
}

/*
 * Creates an array with values the three letter representation for days of the 
 * week and keys the corresponding numeric representation.
 *
 * @return array
 */
function createLookupNumberToDay() {
    $date = strtotime('now');
    $lookup = array();
    for ($i = 1; $i <= 7; $i++) {
        $lookup[date('w', $date)] = date('D', $date);
        $date = strtotime('+1 day', $date);
    }
    return $lookup;
}

/*
 * Converts a string listing days separated by commas into 
 * an array with values the numeric value for the corresponding
 * day of the week.
 *
 * @param string $days
 * @return array
 */
function convertDaysToNumbers($days) {
    $result = array();
    $daysArray = explode(",", str_replace(" ","",$days));
    foreach ($daysArray as $day) {
        $result[] = date('w', strtotime($day));
    }
    return $result;
}

/*
 * Converts the numbers in a string to the corresponding 3-letter day of the
 * week abbreviation.
 *
 * @param string $string
 * @return string
 */
function convertNumbersToDays($string) {
    $lookup = createLookupNumberToDay();
    return str_replace(array_keys($lookup), $lookup, $string);
}

function convert($string) {
    return (convertNumbersToDays(compressNumbers(convertDaysToNumbers($string))));
}

echo convert('mon,tue,wed,thu,fri,sat');
echo '<br />';
echo convert('mon,tue,wed,sat');
echo '<br />';