部署时出现闪亮的应用程序错误，在本地工作（rvest --> html_nodes 问题）答案

【问题标题】：Shiny app error when deployed, works locally (rvest --> html_nodes issue)部署时出现闪亮的应用程序错误，在本地工作（rvest --> html_nodes 问题）
【发布时间】：2016-05-21 20:34:11
【问题描述】：

我有一个 Shiny 应用程序，它从亚特兰大警察局网站下载一个 zip 文件，并将其解压缩为一个临时文件。该应用程序在本地运行良好，但是当我将其部署到 shinyapps.io 时，出现错误： could not find function "xpath_combinedselector"

我把它归结为对 R 包“rvest”、函数“html_nodes”的调用（它使用包“selectr”将 CSS 选择器转换为 XML）。我认为这与 Shiny 端的版本控制有关，但我不知道如何修复它。

作为参考，犯罪数据下载站点是：http://www.atlantapd.org/crimedatadownloads.aspx，我正在使用底部的 zip 文件（每周更新一个不同的 url）：“2009-20yy 犯罪数据文件原始数据 (mm/dd /yyyy)"

代码产生错误：

# load libraries (some of these are used later on in the app, but 
# included here in case they might be the cause)
library(shiny); library(lubridate); library(ggplot2)
library(ggmap); library(RgoogleMaps); library(readr)
library(rvest); library(dplyr)

# Set up temp file to download zip file to
temp <- tempfile()

# Download zip file from location on APD website, to above temp file
download.file(
   read_html("http://www.atlantapd.org/crimedatadownloads.aspx") %>% 
      # THE NEXT LINE IS THE PROBLEM CHILD
      html_nodes("tr:nth-child(15) a") %>% 
      html_attr("href") %>% 
      paste0("http://www.atlantapd.org/", .),
   destfile = temp)

Shiny App 错误日志：

2016-05-21T19:47:43.603137+00:00 shinyapps[103450]: Warning: Error in do.call: could not find function "xpath_combinedselector"
2016-05-21T19:47:43.610211+00:00 shinyapps[103450]: Stack trace (innermost first):
2016-05-21T19:47:43.610213+00:00 shinyapps[103450]:     76: do.call
2016-05-21T19:47:43.610214+00:00 shinyapps[103450]:     75: .self$xpath
2016-05-21T19:47:43.610216+00:00 shinyapps[103450]:     74: selector_to_xpath
2016-05-21T19:47:43.610217+00:00 shinyapps[103450]:     73: FUN
2016-05-21T19:47:43.610218+00:00 shinyapps[103450]:     72: lapply
2016-05-21T19:47:43.610221+00:00 shinyapps[103450]:     69: <Anonymous>
2016-05-21T19:47:43.610222+00:00 shinyapps[103450]:     68: mapply
2016-05-21T19:47:43.610223+00:00 shinyapps[103450]:     67: Map
2016-05-21T19:47:43.610224+00:00 shinyapps[103450]:     66: selectr::css_to_xpath
2016-05-21T19:47:43.610225+00:00 shinyapps[103450]:     65: make_selector
2016-05-21T19:47:43.610226+00:00 shinyapps[103450]:     64: node_find_all
2016-05-21T19:47:43.610227+00:00 shinyapps[103450]:     63: xml_find_all.xml_node
2016-05-21T19:47:43.610220+00:00 shinyapps[103450]:     70: tran$css_to_xpath
2016-05-21T19:47:43.610230+00:00 shinyapps[103450]:     60: html_nodes
2016-05-21T19:47:43.610219+00:00 shinyapps[103450]:     71: sapply
2016-05-21T19:47:43.610232+00:00 shinyapps[103450]:     58: withVisible
2016-05-21T19:47:43.610233+00:00 shinyapps[103450]:     57: freduce
2016-05-21T19:47:43.610234+00:00 shinyapps[103450]:     56: _fseq
2016-05-21T19:47:43.610235+00:00 shinyapps[103450]:     55: eval
2016-05-21T19:47:43.610236+00:00 shinyapps[103450]:     54: eval
2016-05-21T19:47:43.610237+00:00 shinyapps[103450]:     53: withVisible
2016-05-21T19:47:43.610238+00:00 shinyapps[103450]:     52: %>%
2016-05-21T19:47:43.610231+00:00 shinyapps[103450]:     59: function_list[[k]]
2016-05-21T19:47:43.610229+00:00 shinyapps[103450]:     61: html_nodes.default
2016-05-21T19:47:43.610228+00:00 shinyapps[103450]:     62: xml2::xml_find_all
2016-05-21T19:47:43.610242+00:00 shinyapps[103450]:      9: tryCatchList
2016-05-21T19:47:43.610243+00:00 shinyapps[103450]:      8: tryCatch
2016-05-21T19:47:43.610244+00:00 shinyapps[103450]:      7: connect$retry
2016-05-21T19:47:43.610245+00:00 shinyapps[103450]:      6: eval
2016-05-21T19:47:43.610246+00:00 shinyapps[103450]:      5: eval
2016-05-21T19:47:43.610238+00:00 shinyapps[103450]:     13: runApp
2016-05-21T19:47:43.610247+00:00 shinyapps[103450]:      3: eval
2016-05-21T19:47:43.610239+00:00 shinyapps[103450]:     12: fn
2016-05-21T19:47:43.610240+00:00 shinyapps[103450]:     11: doTryCatch
2016-05-21T19:47:43.610241+00:00 shinyapps[103450]:     10: tryCatchOne
2016-05-21T19:47:43.610415+00:00 shinyapps[103450]: Error in do.call(method, list(parsed_selector)) : 
2016-05-21T19:47:43.610248+00:00 shinyapps[103450]:      2: eval.parent
2016-05-21T19:47:43.610247+00:00 shinyapps[103450]:      4: eval
2016-05-21T19:47:43.610249+00:00 shinyapps[103450]:      1: local

【问题讨论】：

标签： r shiny rvest

【解决方案1】：

问题是在为 html_node 函数。这个函数只有一个参数，css OR xpath。

如果您没有指定参数的类型，在您的情况下是 css 选择器，则该参数将被视为 xpath（这就是您得到 error:could not find function "xpath_combinedselector") 。因此，为了确保闪亮的服务器 - 在部署应用程序时 - 识别您提供的参数类型，您应该指定为 html_nodes 参数，如下所示：

 html_nodes(css="tr:nth-child(15) a")

【讨论】：