rvest missing nodes --> NA

问题

I'm trying to search for nodes in an html document using rvest in R. In the code below, I would like to know how return a NULL or NA when "s_BadgeTop*" is missing. It is only for academic purpose.

<div style="margin-bottom:0.5em;"><div><div style="float:left;">Por&nbsp;</div><div style="float:left;"><a href="/gp/pdp/profile/XXX" ><span style = "font-weight: bold;">JOHN</span></a> (UK)  - <a href="/gp/cdp/member-reviews/XXX">Ver todas las opiniones</a><br /><span class="cmtySprite s_BadgeTop1000 " ><span>(TOP 1000 COMENTARISTAS)</span></span></div></div></div>

<div style="margin-bottom:0.5em;"><div><div style="float:left;">Por&nbsp;</div><div style="float:left;"><a href="/gp/pdp/profile/YYY" ><span style = "font-weight: bold;">MARY</span></a> (USA)  - <a href="/gp/cdp/member-reviews/YYY">Ver todas las opiniones</a><br /></div></div></div>

<div style="margin-bottom:0.5em;"><div><div style="float:left;">Por&nbsp;</div><div style="float:left;"><a href="/gp/pdp/profile/ZZZ" ><span style = "font-weight: bold;">CANDICE</span></a> (UK)  - <a href="/gp/cdp/member-reviews/ZZZ">Ver todas las opiniones</a><br /><span class="cmtySprite s_BadgeTop500 " ><span>(TOP 500 COMENTARISTAS)</span></span></div></div></div>

I need a data.frame with this structure:

JOHN (TOP 1000 COMENTARISTAS)
MARY NA
CANDICE (TOP 500 COMENTARISTAS)

I have tried this code:

name <- pg %>%
html_nodes(xpath='//a[contains(@href,"/gp/pdp/profile/")]') %>%
html_text

status <- pg %>%
html_nodes(xpath='//span[contains(@class,"cmtySprite s_BadgeTop")]')  %>% 
html_text
status[is.na(status)] <- "NA"

but status[is.na(status)] <- "NA" does not work.

I get this output:

JOHN (TOP 1000 COMENTARISTAS)
MARY (TOP 500 COMENTARISTAS)
CANDICE (TOP 1000 COMENTARISTAS)

Thanks!

回答1:

You can iterate over each of the three entries, extract name and - potentially the badge - from it, and ultimately merge all your results.

Example:

# For rbindlist
library(data.table)

# Function to parse a particular 'div' and extract name and (potentially) badge
parse_node <- function(node) {
  name <- node %>% 
    html_node('a[href^="/gp/pdp/profile"]') %>%
    html_text
  badge <- node %>%
    html_nodes('span[class*="s_BadgeTop"] span') %>%
    html_text
  list(name=name[1],badge=badge[1])
}

# extract nodes, parse and merge
pg %>%  
  html_nodes('div[style^="margin-bottom"] div div[style^=float]:nth-child(2)') %>%
  lapply(parse_node) %>%
  rbindlist

来源：https://stackoverflow.com/questions/29877451/rvest-missing-nodes-na

标签

parsing

rvest