使用R在一天之内使用4个网址从网站上抓取数据

debugcn 发表于 Dev

丰克-蒙克

我正在尝试从马来西亚环境部的网站上抓取所有历史性的空气污染指数数据，该数据将所有站点的数据分成每天每天4小时的链接，如下所示

http://apims.doe.gov.my/apims/hourly1.php?date=20130701 http://apims.doe.gov.my/apims/hourly2.php?date=20130701

与上面的“ hourly3.php？”相同和“ hourly4.php？”

我对R只是有点熟悉，所以使用XML或scrapeR库最简单的方法是什么？

hrbrmstr

您可以使用列表操作将所有表变成一个宽数据框：

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

date <- 20130701
rng <- c(1:4)

my_tabs <- lapply(rng, function(i) {
  url <- sprintf("http://apims.doe.gov.my/apims/hourly%d.php?date=%s", i, date)
  pg <- html(url)
  pg %>% html_nodes("table") %>% extract2(1) %>% html_table(header=TRUE)
})

glimpse(plyr::join_all(my_tabs, by=colnames(my_tabs[[1]][1:2])))

## Observations: 52
## Variables:
## $ NEGERI / STATE   (chr) "Johor", "Johor", "Johor", "Johor", "Kedah...
## $ KAWASAN/AREA     (chr) "Kota Tinggi", "Larkin Lama", "Muar", "Pas...
## $ MASA/TIME12:00AM (chr) "63*", "53*", "51*", "55*", "37*", "48*", ...
## $ MASA/TIME01:00AM (chr) "62*", "52*", "52*", "55*", "36*", "48*", ...
## $ MASA/TIME02:00AM (chr) "61*", "51*", "53*", "55*", "35*", "48*", ...
## $ MASA/TIME03:00AM (chr) "60*", "50*", "54*", "55*", "35*", "48*", ...
## $ MASA/TIME04:00AM (chr) "59*", "49*", "54*", "54*", "34*", "47*", ...
## $ MASA/TIME05:00AM (chr) "58*", "48*", "54*", "54*", "34*", "45*", ...
## $ MASA/TIME06:00AM (chr) "57*", "47*", "53*", "53*", "33*", "45*", ...
## $ MASA/TIME07:00AM (chr) "57*", "46*", "52*", "53*", "32*", "45*", ...
## $ MASA/TIME08:00AM (chr) "56*", "45*", "52*", "52*", "32*", "44*", ...
## ...

plyr由于与的命名冲突，我很少再实际加载/使用了，dplyr但是join_all非常适合这种情况。

您也可能需要长格式的以下数据：

plyr::join_all(my_tabs, by=colnames(my_tabs[[1]][1:2])) %>% 
  tidyr::gather(masa, nilai, -1, -2) %>%
# better column names
  rename(nigeri=`NEGERI / STATE`, kawasan=`KAWASAN/AREA`) %>%  
# cleanup & convert time (using local timezone)
# make readings numeric; NA will sub for #
  mutate(masa=gsub("MASA/TIME", "", masa), 
         masa=as.POSIXct(sprintf("%s %s", date, masa), format="%Y%m%d %H:%M%p", tz="Asia/Kuala_Lumpur"),
         nilai=as.numeric(gsub("[[:punct:]]+", "", nilai))) -> pollut

head(pollut)
##   nigeri                 kawasan                masa nilai
## 1  Johor             Kota Tinggi 2013-07-01 12:00:00    63
## 2  Johor             Larkin Lama 2013-07-01 12:00:00    53
## 3  Johor                    Muar 2013-07-01 12:00:00    51
## 4  Johor            Pasir Gudang 2013-07-01 12:00:00    55
## 5  Kedah              Alor Setar 2013-07-01 12:00:00    37
## 6  Kedah Bakar Arang, Sg. Petani 2013-07-01 12:00:00    48