如何将这种格式的xml文件读入R？

Question

我正在尝试使用R中的XMLToDataFrame命令来导入xml文件。该命令适用于某些xml文件，但不适用于此文件：

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<reservationDetailsResponse xmlns="http://webservices.sixt.de/webservices/franchise/1.03" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <reservation>
    <reservationNo>983647001</reservationNo>
    <securityCode>381f0977</securityCode>
    <reference1 xsi:nil="true"/>
    <reference2 xsi:nil="true"/>
    <status>RS</status>
    <revision xsi:nil="true"/>
    <language>en_US</language>
    <group>CDM</group>
    <duration>3</duration>
    <voucherDays xsi:nil="true"/>
    <isLongterm>false</isLongterm>
    <hasOwnInsurance>false</hasOwnInsurance>
    <vipStatus xsi:nil="true"/>
    <customerRemark xsi:nil="true"/>
    <stationRemark xsi:nil="true"/>
    <flightNo xsi:nil="true"/>
    <bonusProgramNo xsi:nil="true"/>
    <hasOnlinePaymentGuarantee>false</hasOnlinePaymentGuarantee>
    <origin>
      <dateTime>2016-3-01T01:36:14</dateTime>
      <channel>INTERNET</channel>
    </origin>
    <rate>
      <code>ISU000</code>
      <plan>1</plan>
      <rebate>0</rebate>
      <isPrepaid>false</isPrepaid>
      <corpNo xsi:nil="true"/>
    </rate>
    <pickup>
      <dateTime>2014-07-04T10:00:00</dateTime>
      <station>
        <stationID>895</stationID>
        <name>Reykja</name>
      </station>
    </pickup>
    <return>
      <dateTime>2014-07-07T10:00:00</dateTime>
      <station>
        <stationID>895</stationID>
        <name>Reykjavik</name>
      </station>
    </return>
    <delivery xsi:nil="true"/>
    <collection xsi:nil="true"/>
    <firstDriver>
      <birthday>1957-05-08</birthday>
      <passportNo>462825</passportNo>
      <contact>
        <phone>+1-508-59156</phone>
        <mobile xsi:nil="true"/>
        <email>maria.ursen@gmail.com</email>
        <fax xsi:nil="true"/>
      </contact>
      <license>
        <licenseNo>S658872</licenseNo>
        <date>2014-04-11</date>
        <city>Massetts</city>
        <country xsi:nil="true"/>
      </license>
      <name1>NICSEN</name1>
      <name2>BE</name2>
      <address>
        <street>145 Souttreet</street>
        <zipCode>068</zipCode>
        <city>Upton</city>
        <state>MA</state>
        <country>US</country>
      </address>
    </firstDriver>
    <secondDriver>
      <birthday xsi:nil="true"/>
      <passportNo xsi:nil="true"/>
      <contact xsi:nil="true"/>
      <license xsi:nil="true"/>
      <name1>ADD_DRIVER</name1>
      <name2 xsi:nil="true"/>
      <address xsi:nil="true"/>
    </secondDriver>
    <forbidden xsi:nil="true"/>
    <included xsi:nil="true"/>
    <booked>
      <extra>
        <code>T</code>
        <name>Rentaays</name>
        <booked>1</booked>
        <charged>3</charged>
        <price>
          <currency>EUR</currency>
          <netAmount>62.54</netAmount>
          <vatPercent>24.00</vatPercent>
        </price>
      </extra>
      <extra>
        <code>AD</code>
        <name>Additional driver</name>
        <booked>1</booked>
        <charged>3</charged>
        <price>
          <currency>EUR</currency>
          <netAmount>4.03</netAmount>
          <vatPercent>24.00</vatPercent>
        </price>
      </extra>
    </booked>
    <total>
      <dueAmount>0.00</dueAmount>
      <grossAmount>247.64</grossAmount>
      <vatAmount>47.93</vatAmount>
      <currency>EUR</currency>
      <netAmount>199.71</netAmount>
      <vatPercent>24.00</vatPercent>
    </total>
    <payment>
      <type>VI</type>
      <corpNo xsi:nil="true"/>
      <expressNo xsi:nil="true"/>
      <taxNo xsi:nil="true"/>
      <pickupNativeCurrency xsi:nil="true"/>
      <ccNativeCurrency xsi:nil="true"/>
    </payment>
    <invoice xsi:nil="true"/>
    <split xsi:nil="true"/>
    <prepaid xsi:nil="true"/>
    <voucher xsi:nil="true"/>
    <beneficiary xsi:nil="true"/>
  </reservation>

xml文件中还有许多保留（重复），但我只粘贴了第一部分。我得到的错误是：

Error in `[<-.data.frame`(`*tmp*`, i, names(nodes[[i]]), value = c("9836472687",  : 
  duplicate subscripts for columns

这是我使用命令的方式：

xmlToDataFrame("C:/Users/Davíð Freyr/Documents/xml_file.xml", c("integer", "integer", "numeric"))

我的计划是将多个xml文件导入到R中的一个data.frame中。使用R中的数据并最终将其导入到excel中。他们可能是一个命令，我可以将多个xml文件合并到一个R data.frame吗？

提前致谢