Compound Sum, Length and Average

SassMeister-input.scss

// functions for finding sum, length and averages
// supports complex/compound lists of values
// assumes either no units or identical units

@function compound-sum($args...) {
    $sum: 0;
    @each $arg in $args {
        @if type-of($arg) == list {
            $sum: $sum + compound-sum($arg...);
        } @else {
            $sum: $sum + $arg;
        }
    }
    @return $sum;
}

@function compound-length($args...) {
    $len: 0;
    @each $arg in $args {
        @if type-of($arg) == list {
            $len: $len + compound-length($arg...);
        } @else {
            $len: $len + 1;
        }
    }
    @return $len;
}

@function compound-average($args...) {
    @return compound-sum($args...)/compound-length($args...);    
}

//================================== tests

$test-list: 2 4 6 3, 4 5, 6;

.test {
    sum: compound-sum($test-list, 5);
    len: compound-length($test-list, 5,4);
    avg: compound-average($test-list, 5,9);
    u-sum: compound-sum(1px 2px, 3px 4px);
}

SassMeister-output.css

.test {
  sum: 35;
  len: 9;
  avg: 4.88889;
  u-sum: 10px;
}