xml - 将不均匀的层次列表转换为数据框

Question

我认为这还没有被问到，但是有没有办法将多层次和结构不均匀的列表信息组合成“长”格式的数据框？

具体来说:

library(XML)
library(plyr)
xml.inning <- "http://gd2.mlb.com/components/game/mlb/year_2009/month_05/day_02/gid_2009_05_02_chamlb_texmlb_1/inning/inning_5.xml"
xml.parse <- xmlInternalTreeParse(xml.inning)
xml.list <- xmlToList(xml.parse)
## $top$atbat
## $top$atbat$pitch
##             des              id            type               x               y 
##          "Ball"           "310"             "B"         "70.39"        "125.20" 

结构如下:

> llply(xml.list, function(x) llply(x, function(x) table(names(x))))
$top
$top$atbat
.attrs  pitch 
     1      4 
$top$atbat
.attrs  pitch 
     1      4 
$top$atbat
.attrs  pitch 
     1      5 
$bottom
$bottom$action
     b    des  event      o  pitch player      s 
     1      1      1      1      1      1      1 
$bottom$atbat
.attrs  pitch 
     1      5 
$bottom$atbat
.attrs  pitch 
     1      5 
$bottom$atbat
.attrs  pitch runner 
     1      5      1 
$bottom$atbat
.attrs  pitch runner 
     1      7      1 
$.attrs
$.attrs$num
character(0)
$.attrs$away_team
character(0)
$.attrs$

我想要的是来自 pitch 类别的命名向量的数据框，以及适当的(top、atbat ，<强>底部 )。因此，由于列数不同，我需要忽略不适合 data.frame 的级别。像这样:

   first second third    des     x
1    top  atbat pitch   Ball 70.29
2    top  atbat pitch Strike 69.24
3 bottom  atbat pitch    Out 67.22

有没有一种优雅的方式来做到这一点？谢谢!

Answer 1

我不知道优雅，但这行得通。那些更熟悉 plyr 的人可能会提供更通用的解决方案。

cleanFun <- function(x) {
   a <- x[["atbat"]]
   b <- do.call(rbind,a[names(a)=="pitch"])
   c <- as.data.frame(b)
}
ldply(xml.list[c("top","bottom")], cleanFun)[,1:5]
     .id             des  id type      x
1    top            Ball 310    B  70.39
2    top   Called Strike 311    S 118.45
3    top   Called Strike 312    S  86.70
4    top In play, out(s) 313    X  79.83
5 bottom            Ball 335    B  15.45
6 bottom   Called Strike 336    S  77.25
7 bottom Swinging Strike 337    S  99.57
8 bottom            Ball 338    B 106.44
9 bottom In play, out(s) 339    X 134.76