XQuery Puzzles from Week 1, Day 5, Session 4 of the Advanced Digital Editions NEH Institute at the University of Pittsburgh

convert-date.xqy

xquery version "3.1";

let $date := "July 15, 2022"
let $tokens := fn:tokenize($date, " ")
let $month :=
  switch ($tokens[1]) 
    case "January" return "01"
    case "February" return "02"
    case "March" return "03"
    case "April" return "04"
    case "May" return "05"
    case "June" return "06"
    case "July" return "07"
    case "August" return "08"
    case "September" return "09"
    case "October" return "10"
    case "November" return "11"
    case "December" return "12"
    default return "01"
let $day := $tokens[2] => translate(",","")
let $year := $tokens[3]
return xs:date($year || "-" || $month ||  "-" || $day )

convert-dates.xqy

xquery version "3.1";

for $date in ("July 15, 2022", "January 5, 2023")
let $tokens := fn:tokenize($date, " ")
let $month :=
  switch ($tokens[1]) 
    case "January" return "01"
    case "February" return "02"
    case "March" return "03"
    case "April" return "04"
    case "May" return "05"
    case "June" return "06"
    case "July" return "07"
    case "August" return "08"
    case "September" return "09"
    case "October" return "10"
    case "November" return "11"
    default return "01"
let $day := ($tokens[2] => translate(",","")) ! (if (fn:string-length(.) < 2) then "0" || . else .) 
let $year := $tokens[3]
return xs:date($year || "-" || $month ||  "-" || $day )

convert-roman.xqy

xquery version "3.1";

declare function local:char-to-int($roman as xs:string) as xs:integer {
  switch ($roman)
    case "I" return 1
    case "V" return 5
    case "X" return 10
    case "L" return 50
    case "C" return 100
    case "D" return 500
    case "M" return 1000
    default return 0
};

declare function local:roman-to-integer($roman as xs:string) as xs:integer{
  fn:sum(
    let $symbols := string-to-codepoints($roman) ! codepoints-to-string(.) ! local:char-to-int(.)
    for $symbol at $index in $symbols
    return
      if ($index lt fn:count($symbols))
      then
        let $next-symbol := $symbols[$index + 1]
        return
          if ($symbol ge $next-symbol) then $symbol
          else -$symbol
       else $symbol
)
};

local:roman-to-integer("MDXCIX")

Just to add to the fun, here's a solution that uses windowing. As I mentioned briefly yesterday, XQuery 3.0 added window as a clause to FLWOR expressions. A window allows you to partition your tuple streams. You can use windows to inflect your data, giving structure to data that would otherwise be flat. I use a window clause in this function to capture any pairwise Roman numerals like IV or IX.

xquery version "3.1";

declare function local:convert-roman($roman as xs:string) as xs:integer {
  fn:sum(
    let $symbols as map(xs:string, xs:integer) := map {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000 }
    let $tokens as xs:string+ := string-to-codepoints($roman) ! codepoints-to-string(.)
    let $values as xs:integer+ :=  $tokens ! $symbols(.)
    for tumbling window $w in fn:reverse($values)
        start $start when true() 
        end $end next $next when $next ge $end
    return
      typeswitch($w)
        case xs:integer return $w
        default return $w[1] - $w[2]
  )
};

local:convert-roman("DCCLXXIV")

Right now, window clauses are available in BaseX and Saxon, but not eXistDB. But hopefully, they'll be coming to eXistDB soon!