Question

我必须从网站下载几个表，表格ID为“tabela”，我尝试了各种函数XML::readHTMLTable，XML::xmlTreeParse，但只有rvest个包加载它：

 require(rvest)
 url="http://www.pse.pl/index.php?modul=21&id_rap=2&data=2013-01-01"
 wpkd <- html(url)
 class(wpkd)
[1] "HTMLInternalDocument" "HTMLInternalDocument" "XMLInternalDocument"  "XMLAbstractDocument" 
 str(wpkd)
Classes 'HTMLInternalDocument', 'HTMLInternalDocument', 'XMLInternalDocument', 'XMLAbstractDocument' <externalptr>

现在我想用“tabela”id提取表格或将wpkd保存为纯文本并尝试低级提取。无法正确识别wpkd的结构：

> wpkd %>% xml_structure()
{DTD}
<html>
  <head>
    <title> {text}
    <meta [http-equiv, content]>
    <meta [name, content]>
    <meta [name, content]>
    <link [rel, type, title, href]>
    <meta [name, content]>
    <meta [name, content]>
    <meta [http-equiv, content]>
    <meta [http-equiv, content]>
    <link [rel, type, href]>
    <link [rel, href, type]>
    <link [rel, type, href]>
    <link [rel, href, type, media]>
    <link [rel, href, type, media]>
    <link [rel, href, type, media]>
    <script [src]>
    <script [src]>
Error: Unknown input XMLInternalCommentNode/XMLInternalNode/XMLAbstractNode

Answer 1

鉴于＆＃34;标题＆＃34;不统一（跨越TR s）这是一种方法（它不是唯一的方法）：

library(rvest)
library(magrittr)
library(dplyr)

pg <- html("http://www.pse.pl/index.php?modul=21&id_rap=2&data=2013-01-01")

# small function to extract by column

get_col <- function(doc, i) {
  skip <- ifelse(i==8, -1, -2) # last column is "wonky"
  doc %>% 
    html_nodes(xpath=sprintf("//table[@id='tabela']/tr/td[%d]", i)) %>% 
    extract(-1:skip) %>% # skip the useless "TR"s
    html_text()
}

# manually build data frame, which actually gives you better column names

data.frame(time=pg %>% get_col(1),
           demand=pg %>% get_col(2),
           capacity_jwcd=pg %>% get_col(3),
           capacity_njwcd=pg %>% get_col(4),
           generation_jwcd=pg %>% get_col(5),
           generation_njwcd=pg %>% get_col(6),
           reserve_over=pg %>% get_col(7),
           reserve_below=pg %>% get_col(8),
           stringsAsFactors=FALSE) -> energy

glimpse(energy)

## Observations: 24
## Variables:
## $ time             (chr) "1", "2", "3", "4", "5", "6", "7", "8", "9", "10...
## $ demand           (chr) "14 650", "14 000", "13 325", "12 850", "12 575"...
## $ capacity_jwcd    (chr) "21 032", "21 032", "21 032", "21 032", "21 032"...
## $ capacity_njwcd   (chr) "8 918", "8 918", "8 918", "8 918", "8 918", "8 ...
## $ generation_jwcd  (chr) "7 085", "6 446", "5 777", "5 307", "5 031", "4 ...
## $ generation_njwcd (chr) "7 565", "7 554", "7 548", "7 543", "7 544", "7 ...
## $ reserve_over     (chr) "1 328", "1 269", "1 209", "1 166", "1 141", "1 ...
## $ reserve_below    (chr) "-1 328", "-1 269", "-1 209", "-1 166", "-1 141"...

您需要自己进行类型转换（即使您使用了其中一个自动表功能，您也会这样做。）

从HTMLInternalDocument对象获取R中的表

1 个答案: