Webscraping does not identify the full HTML link - html

Question

My problem is very similar to this one. I want to identify all the HTML links in this website so I can then open the link and download the tables.
The problem is that when I create the extract_links functions as pointed out in that answer, I get a list of all the HTMLs, but this are not complete.
To make it more clear:
If you press "Junio" in year "2022" the real HTML is the following:
http://transparencia.uantof.cl/index.php?action=plantillas_generar_plantilla&ig=21&m=6&a=2022&ia=7658
but the HTML that I am recovering from the source of the website lacks the last bit (&ia=7658):
http://transparencia.uantof.cl/index.php?action=plantillas_generar_plantilla&ig=21&m=6&a=2022
Which does not direct me to the table I want.
The problem is that these numbers do not seem to follow any logic and change between year/month links. Any help on how to retrieve the full HTML links will be greatly appreciated. If you also happen to know how can I retrieve the year/month of the file to add as an extra column that would also be great.
Thanks to the help of #margusl I was able to realize that rvest redirects automatically and that solves my problem.
I am trying to use the following code to loop over different links to obtain the tables, store them in a data frame and then download them:
yr.list <- seq(2019,2020)
mes.list <- seq(1,12)
combined_df <- data.frame()
for (yr in yr.list){
for (mes in mes.list) {
root <- "http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21"
# Full link
url <- paste(root,"&m=",mes,"&a=",yr,sep="")
# Parse HTML File
file<-read_html(url, encoding = "latin1")
file<- rvest::html_table(file)
str(file)
# This is the relevant table
table <- as.data.frame(file[[1]])
# in your loop, add the files that you read to the combined_df
combined_df <- rbind(combined_df, table)
}
}
It does not work because the read_html code with the encoding works only for some years, but not for all. for example, when running:
url <- "http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=3&a=2015"
file<-read_html(url, encoding = "latin1")
It does not recover the tables with names/surnames that recovers in the previous months but something else. Why can't this work on all the sub-pages? Is this a encoding problem again?

Answer 1

If you open that last page you had issues with, you'll see that it serves a sort of a submenu with 2 more links - http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=3&a=2015 . Meaning that it's not enough to just generate links for each month & year and extract first table of each page, all those pages should be checked for content and exceptions should be handled.
Though I took somewhat opportunistic approach and it happened to work with URL range defined in question + those few odd samples, but there could be other surprises down the road. Switched to httr for making requests as it allows to collect and monitor response headers, separating content retrieval and parsing also seems to work around encoding issues, at least in this case. First collecting and then parsing also simplifies debugging, you can check if certain responses / headers were different from the rest (i.e. response length being 10x smaller than average or final, redirected, url differs from the rest). And it's easy to change content handling
/ parsing for a small subset of responses, if needed. If you are not sure what rvest has retrieved, you can always save the response to a html file and check it with browser or editor, something like
html <- read_html(url_or_text_content); write(as.character(html), "dump.html")
library(rvest)
library(httr)
library(purrr)
library(dplyr)
library(tidyr)
library(stringr)
yr.list <- seq(2019,2020)
mes.list <- seq(1,12)
# combine mes.list & yr.list
url.params <- expand.grid(mes = mes.list, yr = yr.list)
# few extra samples:
url.params <- rbind(url.params,
list(mes = 6, yr = 2022), # here rvest strugglest with correct encoding
list(mes = 3, yr = 2015) # returns page with sub-categories
)
url.list <- str_glue("http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m={url.params$mes}&a={url.params$yr}")
url.list
#> http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=1&a=2019
#> http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=2&a=2019
#> http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=3&a=2019
#> ...
#> http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=11&a=2020
#> http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=12&a=2020
#> http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=6&a=2022
#> http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=3&a=2015
# url list for input, output is a tibble with all responses (incl. "url", "date",
# "status_code", header details and response body)
fetch_urls <- function(url.list){
# collect all responses to a list with httr, enable verbose, parse responses later
# add progress bar - requests take a while
resp.list = vector(mode = "list", length = length(url.list))
pb <- txtProgressBar(max = length(url.list), style = 3)
for (i in seq_along(url.list)){
resp.list[[i]] <- GET(url.list[i])
setTxtProgressBar(pb,i)
}
close(pb)
# turn responses into tibble to check urls, response sizes and status codes
resp.tibble <- bind_cols(
map_df(resp.list, ~ .[c("url", "date", "status_code")], .id = "req_id"),
map_df(resp.list, headers) %>% rename_with(~ paste0("header_",.x)),
# map_df(resp_follow.list, "times"),
map_chr(resp.list, content, as = "text") %>% tibble(html_doc = .)
)
return(resp.tibble)
}
resp.tibble <- fetch_urls(url.list)
# check resulting table without html_doc column
# View(resp.tibble[-ncol(resp.tibble)])
resp.tibble %>%
select(req_id:status_code,`header_content-length`) %>%
arrange(`header_content-length`)
#> # A tibble: 26 × 5
#> req_id url date statu…¹ heade…²
#> <chr> <chr> <dttm> <int> <chr>
#> 1 14 http://transparencia.uantof.cl/in… 2022-10-31 17:29:12 200 21371
#> 2 26 http://transparencia.uantof.cl/in… 2022-10-31 17:31:45 200 2230
#> 3 24 http://transparencia.uantof.cl/in… 2022-10-31 17:31:21 200 24035
#> 4 21 http://transparencia.uantof.cl/in… 2022-10-31 17:30:42 200 24173
#> 5 20 http://transparencia.uantof.cl/in… 2022-10-31 17:30:29 200 24183
#> 6 23 http://transparencia.uantof.cl/in… 2022-10-31 17:31:08 200 24184
#> 7 22 http://transparencia.uantof.cl/in… 2022-10-31 17:30:55 200 24207
#> 8 18 http://transparencia.uantof.cl/in… 2022-10-31 17:30:04 200 24405
#> 9 16 http://transparencia.uantof.cl/in… 2022-10-31 17:29:38 200 24715
#> 10 7 http://transparencia.uantof.cl/in… 2022-10-31 17:27:32 200 24716
#> # … with 16 more rows, and abbreviated variable names ¹​status_code,
#> # ²​`header_content-length`
# 26. is kind of suspicious:
# 25 http://transparencia.uantof.cl/index.php?action=plantillas_generar_plantilla&ig=21&m=6&a=2022&ia=76…
# 26 http://transparencia.uantof.cl/index.php?action=plantillas_selec_archivo&ig=21&m=3&a=2015
# looks like there has been no redirection and its header_content-length is about 10x smaller than for other responses
# checking it more closely reveals that the page includes a "submenu" instead of table(s):
# <p class="subMenu_interiores">
# <b>2015 - Marzo</b>
# ABRIL 2015
# Marzo 2015
# </p>
# lets' collect urls that were not redirected from our tibble and harvest links from stored html:
suburl.list <- resp.tibble %>%
# urls that do NOT include "plantillas_generar_plantilla"
filter(!str_detect(url, "plantillas_generar_plantilla")) %>%
pull(html_doc) %>%
# rvest does not like lists, thus let's map()
map( ~ read_html(.x) %>% html_elements("#columna1_interiores a") %>% html_attr("href")) %>%
unlist() %>%
paste0("http://transparencia.uantof.cl/",.)
suburl.list
#> [1] "http://transparencia.uantof.cl/index.php?action=plantillas_generar_plantilla&ig=21&m=3&a=2015&ia=772"
#> [2] "http://transparencia.uantof.cl/index.php?action=plantillas_generar_plantilla&ig=21&m=3&a=2015&ia=648"
# fetch content from those submenu urls
subresp.tibble <- fetch_urls(suburl.list)
# sanity check:
subresp.tibble %>%
select(req_id:status_code,`header_content-length`)
#> # A tibble: 2 × 5
#> req_id url date statu…¹ heade…²
#> <chr> <chr> <dttm> <int> <chr>
#> 1 1 http://transparencia.uantof.cl/ind… 2022-10-31 17:31:52 200 25385
#> 2 2 http://transparencia.uantof.cl/ind… 2022-10-31 17:31:59 200 25332
#> # … with abbreviated variable names ¹​status_code, ²​`header_content-length`
# better, sizes align with previous results.
# collect all relevant responses
table_1 <- resp.tibble %>%
filter(str_detect(url, "plantillas_generar_plantilla")) %>%
bind_rows(subresp.tibble) %>%
# extract html (as strings)
pull(html_doc) %>%
# rvest does not like lists, thus let's map(), pluck(1) extracts first table (from each page)
map(~ read_html(.x) %>% html_table() %>% pluck(1)) %>%
# first attempt to bind rows fails, aparently column types differ
# change all non-character columns to character
map (~ mutate(.x, across(!where(is.character),as.character))) %>%
# bind all tables by rows
bind_rows()
# columns vary across tables so number of NA fields in final result is rather high
Final result for 26 pages, a 10,987 × 30 tibble:
table_1
#> # A tibble: 10,987 × 30
#> Nº PLANTA PATERNO MATERNO NOMBRES G TITULO CARGO REGION ASIGN…¹
#> <chr> <chr> <chr> <chr> <chr> <chr> <chr> <chr> <chr> <chr>
#> 1 1 DIRECTIVO ABARZA CASTRO JESSIC… 6 ADMIN… JEFE… SEGUN… (1)(8)…
#> 2 2 PROFESIONAL ABASOLO QUINTE… NURY D… 12 EDUCA… PROF… SEGUN… (4)(8)…
#> 3 3 ACADEMICO ACOSTA PENA ROXANA… 11 EDUCA… PROF… SEGUN… (2)(8)…
#> 4 4 AUXILIARES ACOSTA PIZARRO ROBERT… 23 LICEN… AUXI… SEGUN… (7)(8)…
#> 5 5 DIRECTIVO AGENO SIERRA ROSELL… 4 MATRO… DIRE… SEGUN… (1)(8)…
#> 6 6 AUXILIARES AGUIRRE LAZO RENE G… 16 LICEN… AUXI… SEGUN… (7)(8)…
#> 7 7 TECNICOS ALAMOS MARIN SERGIO… 13 TECNI… TECN… SEGUN… (5)(8)…
#> 8 8 AUXILIARES ALAYANA CORTES CHRIST… 23 LICEN… AUXI… SEGUN… (7)(8)…
#> 9 9 ACADEMICO ALCOTA AGUIRRE PATRIC… 9 ING. … PROF… SEGUN… (2)(8)…
#> 10 10 ADMINISTRATI… ALFARO BARRAZA MARIA … 23 LICEN… ADMI… SEGUN… (6)(8)…
#> # … with 10,977 more rows, 20 more variables: `UNID MONETARIA` <chr>,
#> # `REMUNERACION MENSUAL BRUTA` <chr>, HORAS <chr>, `CANT. HORAS` <chr>,
#> # `MONTO HORAS EXTRAS` <chr>, `FECHA DE INGRESO` <chr>, `F. HASTA` <chr>,
#> # OBSERVACIONES <chr>, GRADO <chr>, ESTAMENTO <chr>,
#> # `Apellido Paterno` <chr>, `Apellido Materno` <chr>, Nombres <chr>,
#> # `Grado ERUA` <chr>, `CALIFICACION PROFESIONAL O FORMACION` <chr>,
#> # `CARGO O FUNCION` <chr>, `R BRUTA` <chr>, `Horas Extras` <chr>, …
Created on 2022-10-31 with reprex v2.0.2