Question

我想从这个html中选择：

doc <- htmlParse("http://eusoils.jrc.ec.europa.eu/ESDB_Archive/ESDBv3/legend/sg_attr.htm")

但我遇到一些特殊字符问题（即＆gt;和＆lt;符号）并得到不同长度的节点，请看这里：

legs <- getNodeSet(doc, "//a")
leg_names <- sapply(legs, xmlGetAttr, "name")
leg_descr <- xpathSApply(doc, "//strong", xmlValue)

# not the same length??
cbind(leg_names, leg_descr)

# different length??
getNodeSet(doc, '//text()[following-sibling::a]')

和

# why is this not working?
getNodeSet(doc, '//a[@name="AGLIM1"]/text()[following-sibling::strong')

最后我想在一个有两列的表中包含每个图例（带有特定名称的标签后面的文本），第一个带有值/符号，第二个带有标签。

喜欢这个WRB-FULL：

     Value                  Label
        AB            Albeluvisol
      ABal       Alic Albeluvisol
      ABap   Abruptic Albeluvisol
      ABar     Arenic Albeluvisol
      ABau     Alumic Albeluvisol
     ABeun Endoeutric Albeluvisol
       ...        ...         ...

Answer 1

文档的格式不一致：有<a>个元素没有跟随<strong>元素 - 所以还有更多的前者。

cbind( head(leg_names,8), head(leg_descr,8) )
     [,1]            [,2]                                                                                                    
# [1,] "AGLIM1"        "AGLIM1: Code of the most important limitation to agricultural use of the STU"                          
# [2,] "AGLIM2"        "AGLIM2: Code of a secondary limitation to agricultural use of the STU"                                 
# [3,] "BORDER_SOIL1M" "FAO85-FULL: Full Soil Code 1974 FAO"                                                                   
# [4,] "SOIL1M"        "FAO85-LEV1: Soil major group code of the STU from the 1974 (modified CEC 1985) FAO-UNESCO Soil Legend" 
# [5,] "CFL"           "FAO85-LEV2: Second level soil code of the STU from the 1974 (modified CEC 1985) FAO-UNESCO Soil Legend"
# [6,] "CL"            "FAO85-LEV3: Third level soil code of the STU from the 1974 (modified CEC 1985) FAO-UNESCO Soil Legend" 
# [7,] "COUNTRY"       "FAO90-FULL:Full soil code of the STU from the 1990 FAO-UNESCO Soil Legend"                             
# [8,] "FAO85FU"       "FAO90-LEV1: Soil major group code of the STU from the 1990 FAO-UNESCO Soil Legend"

following-sibling方法看起来更有希望，但由于<a>元素没有立即跟随<strong>元素，因此您最终可能会得到另一个元素的描述。

getNodeSet(doc, '//a[@name="AGLIM1"]/following-sibling::strong/text()')[[1]]

另一种方法是忘记格式化并将文件视为文本文件。

raw_data <- readLines("http://eusoils.jrc.ec.europa.eu/ESDB_Archive/ESDBv3/legend/sg_attr.htm")
library(stringr)
matches <- str_extract(raw_data, '<a .*<strong>.*')
matches <- matches[ ! is.na(matches) ]
result <- str_match(matches, '<a name="(.*?)".*<strong>(.*)</strong>')[,-1]
head(result)
     [,1]       [,2]                                                                                                    
[1,] "AGLIM1"   "AGLIM1: Code of the most important limitation to agricultural use of the STU"                          
[2,] "AGLIM2"   "AGLIM2: Code of a secondary limitation to agricultural use of the STU"                                 
[3,] "FAO85FU"  "FAO85-FULL: Full Soil Code 1974 FAO"                                                                   
[4,] "FAO85LV1" "FAO85-LEV1: Soil major group code of the STU from the 1974 (modified CEC 1985) FAO-UNESCO Soil Legend" 
[5,] "FAO85LV2" "FAO85-LEV2: Second level soil code of the STU from the 1974 (modified CEC 1985) FAO-UNESCO Soil Legend"
[6,] "FAO85LV3" "FAO85-LEV3: Third level soil code of the STU from the 1974 (modified CEC 1985) FAO-UNESCO Soil Legend"

兄弟姐妹之后的R XPath文本

1 个答案: