Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.2)
// Compass (v1.0.0.alpha.17)
// ----

// Counts the number of occurrences of each value of $list
// -------------------------------------------------------------------------------
// @param $list [List] : list
// -------------------------------------------------------------------------------
// @return [Map]

@function count-values($list) {
  $map: ();

  @each $item in $list {
    $index: map-get($map, $item);
    $value: if($index, $index + 1, 1);
    $map: map-merge($map, ($item: $value));
  }

  @return $map;
}

$list: test string banana abc string a banana test;
$count: count-values($list);

sass {
  count-values: inspect($count); 
}

SassMeister-output.css

sass {
  count-values: (test: 2, string: 2, banana: 2, abc: 1, a: 1);
}