不需要rvest 或会话。下面的函数将接受电台和日期，并返回一个数据框，其中包含 USGS 每次下载时吐出的数据文件注释。
它使用“下载压缩文件”选项来节省带宽并加快下载速度。它会生成临时文件来读取数据，但会自行清理。列被转换为正确的类型（不过，如果你愿意，你可以省略那部分代码）。如果不需要，也可以省略附加的注释（它似乎对我有用）。
readr::read_lines() 用于提高速度，如果您不想依赖 readr 包，可以使用 readLines()。
将data.frame 转换为tibble 版本主要是为了更好地打印，但它还有其他潜在优势，因此如果您不想依赖tibble 包，也可以省略它。
有一个硬编码的 99 秒超时，但您可以根据需要对其进行参数化。
library(httr)
library(readr)
library(tibble)
#' Retrieve IDA Station Data
#'
#' @param site_no site id
#' @param date_from records from date YYYY-mm-dd
#' @param date_to records to date YYYY-mm-dd
#' @return a parsed, type-converted data frame with a comments attribute.
#' @example
#' deerfield <- get_ida("01170000", "1990-10-01", "2007-09-30")
#'
#' head(deerfield)
#'
#' cat(comment(deerfield))
get_ida <- function(site_no, date_from, date_to) {
date_from_time <- sprintf("%s 00:15:00.0", date_from)
date_to_time <- sprintf("%s 23:45:00.0", date_to)
ida_referer <- sprintf("http://ida.water.usgs.gov/ida/available_records.cfm?sn=%s", site_no)
tf <- tempfile(".zip")
res <- POST(url = "http://ida.water.usgs.gov/ida/available_records_process.cfm",
body = list(fromdate = date_from,
todate = date_to,
mindatetime = date_from_time,
maxdatetime = date_to_time,
site_no = site_no,
rtype = "2",
submit1 = "Retrieve+Data"),
add_headers(Origin="http://ida.water.usgs.gov",
Referer=ida_referer),
write_disk(tf),
timeout(99),
encode = "form")
fils <- unzip(tf, exdir=tempdir())
tmp <- read_lines(fils)
unlink(tf)
unlink(fils)
comments <- grep("^#", tmp, value=TRUE)
records <- grep("^#", tmp, value=TRUE, invert=TRUE)
header <- records[1:2]
records <- records[-(1:2)]
cols <- strsplit(header[1], "[[:space:]]+")[[1]]
comments <- paste0(comments, collapse="\n")
records <- paste0(records, collapse="\n")
df <- read_tsv(records, col_names=cols, "cccnnnnc")
df$date_time <- as.POSIXct(df$date_time, format="%Y%m%d%H%M%S")
df <- as_tibble(df)
comment(df) <- comments
df
}
证明它有效：
deerfield <- get_ida("01170000", "1990-10-01", "2007-09-30")
dplyr::glimpse(deerfield)
## Observations: 550,917
## Variables: 8
## $ site_no <chr> "01170000", "01170000", "01170000", "01170000", "0117000...
## $ date_time <time> 1990-10-01 00:15:00, 1990-10-01 00:30:00, 1990-10-01 00...
## $ tz_cd <chr> "EDT", "EDT", "EDT", "EDT", "EDT", "EDT", "EDT", "EDT", ...
## $ dd <dbl> 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,...
## $ accuracy_cd <dbl> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,...
## $ value <dbl> 146, 139, 135, 143, 154, 166, 171, 175, 171, 166, 162, 1...
## $ prec <dbl> 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,...
## $ remark <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, ...
head(deerfield)
## # A tibble: 6 x 8
## site_no date_time tz_cd dd accuracy_cd value prec remark
## <chr> <time> <chr> <dbl> <dbl> <dbl> <dbl> <chr>
## 1 01170000 1990-10-01 00:15:00 EDT 7 1 146 3 <NA>
## 2 01170000 1990-10-01 00:30:00 EDT 7 1 139 3 <NA>
## 3 01170000 1990-10-01 00:45:00 EDT 7 1 135 3 <NA>
## 4 01170000 1990-10-01 01:00:00 EDT 7 1 143 3 <NA>
## 5 01170000 1990-10-01 01:15:00 EDT 7 1 154 3 <NA>
## 6 01170000 1990-10-01 01:30:00 EDT 7 1 166 3 <NA>
cat(comment(deerfield))
# retrieved: 2016-09-12 05:32:34 CST
#
# Data for the following station is contained in this file
# ---------------------------------------------------------
# USGS 01170000 DEERFIELD RIVER NEAR WEST DEERFIELD, MA
#
# This data file was retrieved from the USGS
# instantaneous data archive at
# http://ida.water.usgs.gov
#
# ---------------------WARNING---------------------
# The instantaneous data you have obtained from
# this automated U.S. Geological Survey database
# may or may not have been the basis for the published
# daily mean discharges for this station. Although
# automated filtering has been used to compare these
# data to the published daily mean values and to remove
# obviously bad data, there may still be significant
# error in individual values. Users are strongly
# encouraged to review all data carefully prior to use.
# These data are released on the condition that neither
# the USGS nor the United States Government may be held
# liable for any damages resulting from its use.
#
# This file consists of tab-separated columns of the
# following fields.
#
# column column definition
# ----------- -----------------------------------------
# site_no USGS site identification number
# date_time date and time in format (YYYYMMDDhhmmss)
# tz_cd time zone
# dd internal USGS sensor designation (''data descriptor'')
# accuracy_cd accuracy code
# 0 - A daily mean discharge calculated from the instantaneous
# data on this day is 0.01 cubic feet per second
# or less and the published daily mean is zero.
# 1 - A daily mean discharge calculated from the instantaneous
# data on this day matches the published daily mean
# within 1 percent.
# 2 - A daily mean discharge calculated from the instantaneous
# data on this day matches the published daily mean
# from greater than 1 to 5 percent.
# 3 - A daily mean discharge calculated from the instantaneous
# values on this day matches the published daily mean
# from greater than 5 to 10 percent.
# 9 - The instantaneous value is considered correct by the
# collecting USGS Water Science Center. A published daily
# mean value does not exist and/or no comparison was made.
# value discharge in cubic feet per second
# precision digits of precision in the discharge
# remark optional remark code
# Remark Explanation
# < Actual value is known to be less than reported value.
# > Actual value is known to be greater than reported value.
# & Value is affected by unspecified reasons.
# A Value is affected by ice at the measurement site.
# B Value is affected by backwater at the measurement site.
# e Value has been estimated by USGS personnel.
# E Value was computed from an estimated value.
# F Value was modified due to automated filtering.
# K Value is affected by instrument calibration drift.
# R Rating is undefined for this value.
#
#