illustration of mapreduce using xquery 3.0 word count example

gistfile1.txt

xquery version "3.0";

declare function local:mapReduce(
  $list as item()*,
  $mapper as function(*),
  $reducer as function(*)
)
{
let $intermediate := for $l at $pos in $list return $mapper("list" || $pos,$l)
return
  for $key in distinct-values($intermediate/key)
  return $reducer($key, $intermediate[key eq $key])
};

let $list := ("The quick brown fox jumped over the lazy grey dogs.","That's one small step for a man, one giant leap for mankind.","Mary had a little lamb, Its fleece was white as snow; And everywhere that Mary went, The lamb was sure to go.")

return 
local:mapReduce(
  $list, 
  function($key,$value){for $w in tokenize($value,' ') return <item list="{$key}"><key>{replace($w,"(\.|,|;)","")}</key><value>1</value></item>},
  function($key,$values){<item lists="{distinct-values($values/@list)}"><key>{$key}</key><value>{sum($values/value)}</value></item>}
)