问题描述:

I'm trying to retrieve the Medals Table inside Wikipedia for Olympics 2012.

library(rvest)

library(magrittr)

url <- "https://en.wikipedia.org/wiki/United_States_at_the_2012_Summer_Olympics"

xpath0 <- '//*[@id="mw-content-text"]/table[1]'

xpath1 <- '//*[@id="mw-content-text"]/table[2]'

xpath2 <- '//*[@id="mw-content-text"]/table[2]/tbody/tr/td[1]'

xpath3 <- '//*[@id="mw-content-text"]/table[2]/tbody/tr/td[1]/table'

tb <- url %>%

html() %>%

html_nodes(xpath=xpath0) %>%

html_nodes("") %>%

html_table()

xpath0 or xpath1 return an error

Error in parse_simple_selector(stream) :

Expected selector, got <EOF at 1>

xpath2 and xpath3 return empty lists.

At same time I tried to use Selectorgadget (https://cran.r-project.org/web/packages/rvest/vignettes/selectorgadget.html) to point to the exact element. I got

//td[(((count(preceding-sibling::) + 1) = 1) and parent::)] |

//*[contains(concat( " ", @class, " " ), concat( " ",

"headerSortDown", " " ))]

and the Error

Error in parse_simple_selector(stream) :

Expected selector, got

I really appreciate any help.

Joa

网友答案:

The first table with the names has a complicated structure and seems to be very difficult to convert into a standard format. At least I didn't succeed.

A summary of the number of medals by sport and the total medals can be obtained with

library(rvest) #v.0.2.0.9000
url <- "https://en.wikipedia.org/wiki/United_States_at_the_2012_Summer_Olympics" 
tb <- read_html(url) %>% html_node("table.wikitable:nth-child(2)") %>% html_table(fill=TRUE)
#> head(tb)
#   Medals by sport   NA   NA   NA    NA NA NA
#1            Sport 01 ! 02 ! 03 ! Total NA NA
#2         Swimming   16    9    6    31 NA NA
#3    Track & field    9   12    7    28 NA NA
#4       Gymnastics    3    1    2     6 NA NA
#5         Shooting    3    0    1     4 NA NA
#6           Tennis    3    0    1     4 NA NA

Then there is another table summarizing all competitors that you can get with

tb2 <- read_html(url) %>% html_node("table.wikitable:nth-child(20)") %>% html_table()
#> head(tb2)
#                        Sport Men Women Total
#1                     Archery   3     3     6
#2 Athletics (track and field)  63    62   125
#3                   Badminton   2     1     3
#4                  Basketball  12    12    24
#5                      Boxing   9     3    12
#6                    Canoeing   5     2     7

And this is the table of multiple medalists:

tb3 <- read_html(url) %>%  html_node("table.wikitable:nth-child(8)") %>% html_table(fill=TRUE)
#> head(tb3)
#  Multiple medalists            NA   NA   NA   NA    NA NA
#1               Name         Sport 01 ! 02 ! 03 ! Total NA
#2     Michael Phelps      Swimming    4    2    0     6 NA
#3     Missy Franklin      Swimming    4    0    1     5 NA
#4    Allison Schmitt      Swimming    3    1    1     5 NA
#5        Ryan Lochte      Swimming    2    2    1     5 NA
#6      Allyson Felix Track & field    3    0    0     3 NA

It really depends on which table you want to have, as pointed out by @Metrics. There are many tables on that page.

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