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r - 从 xml2 和 rvest 子集 data.frame 出错

问题描述

我正在从维基百科抓取数据并将其放入 data.frame 中。但是，我不能对生成的 data.frame 进行子集化。

如果我使用 dput 将数据重新加载到另一个变量中，那么子集就可以正常工作。我不清楚我是否做错了什么，或者 R 或我正在使用的某个包中是否存在错误。这是一个可重现的示例。

第 1 步：将数据加载到reps

library(rvest)
library(xml2)
url    = "https://en.m.wikipedia.org/wiki/List_of_current_members_of_the_United_States_House_of_Representatives"
file   = xml2::read_html(url)
tables = rvest::html_nodes(file, "table")

reps = rvest::html_table(tables[6])
reps = as.data.frame(reps)[1,1:3]

reps$District
# [1] "Alabama 1"

# I expected this line to return TRUE
reps$District == "Alabama 1"
# [1] FALSE

# Because the above line returns FALSE, this code returns an empty data.frame
reps[reps$District=="Alabama 1",]
# [1] District Member   Party   
# <0 rows> (or 0-length row.names)

特别奇怪的是，如果我使用 dput 写入和重新加载数据，子集可以正常工作：

dput(reps)
# structure(list(District = "Alabama 1", Member = "Bradley Byrne", 
#    Party = NA), row.names = 1L, class = "data.frame")

x=structure(list(District = "Alabama 1", Member = "Bradley Byrne", 
                 Party = NA), row.names = 1L, class = "data.frame")

# now it's TRUE!
x$District=="Alabama 1"
# [1] TRUE

# and so the subset works
x[x$District == "Alabama 1", ]
# District        Member Party
# 1 Alabama 1 Bradley Byrne    NA

我相信我正在使用最新版本的 R 和所有软件包：

> sessionInfo()
R version 4.0.2 (2020-06-22)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Catalina 10.15.5

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] httr_1.4.2     compiler_4.0.2 selectr_0.4-2  magrittr_1.5   R6_2.4.1       tools_4.0.2   
 [7] curl_4.3       xml2_1.3.2     stringi_1.4.6  stringr_1.4.0  rvest_0.3.6

标签： rrvestxml2

解决方案

\u00A0将匹配&nbsp;，因此您可以将所有这些替换为gsub.

reps$District <- gsub("\u00A0", " ", reps$District, fixed = TRUE)

完整代码：

library(rvest)
library(xml2)
url    = "https://en.m.wikipedia.org/wiki/List_of_current_members_of_the_United_States_House_of_Representatives"
file   = xml2::read_html(url)
tables = rvest::html_nodes(file, "table")
reps = rvest::html_table(tables[6])
reps = as.data.frame(reps)[1,1:3]
reps$District <- gsub("\u00A0", " ", reps$District, fixed = TRUE)
reps$District == "Alabama 1"
# [1] TRUE

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