Ruby REXML如何获取模式中的第一个同级

我试图解析MLB GameDay中可用的信息。下面是我正在使用的一个示例文件：

具体来说，下面是一个XML输出示例：

<bottom>
<action b="0" s="0" o="0" des="Kole Calhoun remains in the game as the right fielder. " des_es="Kole Calhoun permanece en el juego como el jardinero derecho. " event="Defensive Switch" tfs="010840" tfs_zulu="2014-04-06T01:08:40Z" player="594777" pitch="5"/>
<atbat num="50" b="4" s="0" o="0" start_tfs="010846" start_tfs_zulu="2014-04-06T01:08:46Z" batter="514888" pitcher="572140" des="Jose Altuve walks. " des_es="Jose Altuve recibe base por bolas. " event="Walk" b1="514888" b2="" b3="">
<pitch sv_id="140405_200702" des="Ball" des_es="Bola mala" type="B" start_speed="90.6" pitch_type="FT"/>
<pitch sv_id="140405_200718" des="Ball" des_es="Bola mala" type="B" start_speed="90.8" pitch_type="FF"/>
<pitch sv_id="140405_200738" des="Ball" des_es="Bola mala" type="B" start_speed="91.5" pitch_type="FT"/>
<pitch sv_id="140405_200757" des="Ball" des_es="Bola mala" type="B" start_speed="90.2" pitch_type="FF"/>
</atbat>
<atbat num="51" b="1" s="1" o="2" start_tfs="011113" start_tfs_zulu="2014-04-06T01:11:13Z" batter="461882" pitcher="572140" des="Jesus Guzman grounds into a double play, third baseman John McDonald to second baseman Howie Kendrick to first baseman Albert Pujols. Jose Altuve out at 2nd. " des_es="Jesus Guzman batea rodado batea para doble matanza, tercera base John McDonald a segunda base Howie Kendrick a primera base Albert Pujols. Jose Altuve a cabo a 2da. " event="Grounded Into DP" b1="" b2="" b3="">
<pitch sv_id="140405_200849" des="Called Strike" des_es="Strike cantado" type="S" start_speed="90.2" pitch_type="FT"/>
<pitch sv_id="140405_200915" des="Ball" des_es="Bola mala" type="B" start_speed="74.0" pitch_type="CU"/>
<pitch sv_id="140405_200941" des="In play, out(s)" des_es="En juego, out(s)" type="X" start_speed="83.7" pitch_type="CH"/>
</atbat>
<atbat num="52" b="2" s="3" o="3" start_tfs="011242" start_tfs_zulu="2014-04-06T01:12:42Z" batter="474892" pitcher="572140" des="Chris Carter called out on strikes. " des_es="Chris Carter se poncha sin tirarle. " event="Strikeout" b1="" b2="" b3="">
<pitch sv_id="140405_201027" des="Ball" des_es="Bola mala" type="B" start_speed="73.5" pitch_type="CU"/>
<pitch sv_id="140405_201044" des="Ball" des_es="Bola mala" type="B" start_speed="91.2" pitch_type="FT"/>
<pitch sv_id="140405_201111" des="Called Strike" des_es="Strike cantado" type="S" start_speed="91.1" pitch_type="FT"/>
<pitch sv_id="140405_201132" des="Swinging Strike" des_es="Strike tirándole" type="S" start_speed="91.6" pitch_type="FT"/>
<pitch sv_id="140405_201155" des="Called Strike" des_es="Strike cantado" type="S" start_speed="92.5" pitch_type="FT"/>
</atbat>
</bottom>

理想情况下，

Action#init

将有一个名为

atbat

的新初始值设定项。问题是，如何获取我正在实例化的

操作

之后的

第一个atbat标记

在上面的示例中，如果我要抓取第一个

操作

，它还应该能够抓取下一个

atbat

兄弟，如下所示：

<atbat num="50" b="4" s="0" o="0" start_tfs="010846" start_tfs_zulu="2014-04-06T01:08:46Z" batter="514888" pitcher="572140" des="Jose Altuve walks. " des_es="Jose Altuve recibe base por bolas. " event="Walk" b1="514888" b2="" b3="">

这是未经测试的（我使用并建议使用它来解析XML），但应该可以：

@xml_doc.elements.each("inning/bottom/action") { |element| 
  at_bat = REXML::XPath.first(elem, 'following-sibling::atbat[1]')
  action = Action.new
  action.init(element, at_bat, @gid, @num)
  @bottom_actions.push action
}
# ...

---

使用现有项目，因此使用REXML。尝试了上述方法，虽然没有任何错误，但at_bat返回

nil

我已编辑了我的答案。您应该使用下面描述的

同级
XPath轴来获取第一个“atbat”元素。没问题！
[1]
第一个XPath选择器可能是多余的，但是，根据REXML内部的工作方式，可能是必要的，或者可能提供更好的性能。
@xml_doc.elements.each("inning/bottom/action") { |element| 
  at_bat = REXML::XPath.first(elem, 'following-sibling::atbat[1]')
  action = Action.new
  action.init(element, at_bat, @gid, @num)
  @bottom_actions.push action
}
# ...