使用 R 解析 BGG xml api 中的 xml 数据

问：

这个问题是这个问题的第二部分：如何在 R 中为 BGG API 解析 xml 列表和表。

我想为此表生成一个数据框：

<marketplacelistings>
  <listing>
    <listdate>Thu, 19 Jan 2006 22:08:15 +0000</listdate>
    <price currency="EUR">90.00</price>
    <condition>likenew</condition>
    <notes>Siedler von Catan / Settlers of Catan-Set (Basisspiel/basic game + Erweiterungen Die Seefahrer/ Städte und Ritter/ 5-6 Spieler / extensions The Seafarers/ Cities and Knights/ 5-6 players); 3 x gespielt (Neuwertig; lediglich alle Bestandteile in EINER der Originalboxen verstaut) / 3 times played (like new; only all items in ONE original box stored); Abgabe nur komplett / selling only all together; KEIN Festpreis (nur um überhaupt etwas einzugeben) – erwarte Angebot! / no fixed price (just to complete the entries)– make an offer; Versand weltweit zu Lasten Käufer / shipping worldwide, paid by buyer</notes>
    <link href="https://boardgamegeek.com/market/product/40605" title="marketlisting"/>
  </listing>
  <listing>
    <listdate>Mon, 29 Sep 2008 15:25:32 +0000</listdate>
    <price currency="USD">34.95</price>
    <condition>new</condition>
    <notes>Brand New Sealed Board Game. Released from MayFair Games. Price is in USD. If you wish to pay in CAD...then we will convert at market rate. Shipping is $10.95 USD. We also carry the 5-6 Player Expansion that goes with this for $24.95 USD. We have sold thousands of board games across Canada. Please feel free to buy with confidence.</notes>
    <link href="https://boardgamegeek.com/market/product/116347" title="marketlisting"/>
  </listing>

这是我不知道该怎么办的地方。这个游戏大约有 100 个列表，我想从中制作一个数据框。我从哪里开始？下面的代码不起作用，因为它给出了 为 NULL 结果。

listings_df <- do.call(rbind,lapply(
  getNodeSet(xmltop, '//marketplacelistings'),
  function(x) data.frame(
    XML:::xmlAttrsToDataFrame(xmlChildren(x)),
    row.names = NULL
  )))

这个问题的完整文件在这里： https://boardgamegeek.com/xmlapi/boardgame/13&type=boardgame,boardgameexpansion,boardgameaccesory,rpgitem,rpgissue,videogame&versions=1&stats=1&videos=1&marketplace=1&comments=1

编辑：这是我的最终解决方案。它可能不优雅，但它有效。

marketplace_df_func <- function(xmltop){

 marketplace_df <- data.frame(
listdate = xmlSApply(getNodeSet(xmltop, "//marketplacelistings//listing//listdate"), xmlValue),
currency = xmlSApply(getNodeSet(xmltop, "//marketplacelistings//listing//price[@currency]"), xmlAttrs),
price = xmlSApply(getNodeSet(xmltop, "//marketplacelistings//listing//price"), xmlValue),
condition = xmlSApply(getNodeSet(xmltop, "//marketplacelistings//listing//condition"), xmlValue))

marketplace_df$listdate <- substr(marketplace_df$listdate, 1, 25)

return(marketplace_df)}