Skip to content
Be nice on the web
Branch: master
Clone or download
dmi3kno Merge pull request #13 from gregrs-uk/gregrs-doc
Minor improvements to docs / error messages
Latest commit 445bf49 Dec 18, 2018
Permalink
Type Name Latest commit message Commit time
Failed to load latest commit information.
R Minor improvements to docs / error messages Dec 18, 2018
data-raw
man
tests removed memoise of robotstxt and added warnings about unscrapable url Jul 28, 2018
.Rbuildignore Release v0.0.0.9001 Jul 27, 2018
.gitignore
DESCRIPTION
LICENSE Release v0.0.0.9001 Jul 27, 2018
LICENSE.md
NAMESPACE
NEWS.md release v.0.0.0.9005 added html_attrs_dfr and rip Aug 10, 2018
README.Rmd Minor improvements to docs / error messages Dec 18, 2018
README.md
polite.Rproj Initial commit Jul 23, 2018

README.md

polite

The goal of polite is to promote responsible web etiquette.

“bow and scrape” (verb):

  1. To make a deep bow with the right leg drawn back (thus scraping the floor), left hand pressed across the abdomen, right arm held aside.

  2. (idiomatic, by extension) To behave in a servile, obsequious, or excessively polite manner. [1]
    Source: Wiktionary, The free dictionary

The package’s two main functions bow and scrape define and realize web harvesting session. bow is used to introduce the client to the host and ask for permission to scrape (by inquiring against host’s robots.txt file), while scrape is the main function for retrieving data from the remote server. Once the connection is established, there’s no need to bow again. Rather, in order to adjust a scraping url the user can simply nod to the new path, which updates the session’s url, making sure that the new location can be negotiated against robots.txt

The three pillars of polite session are seeking permission, taking slowly and never asking twice.

The package builds on awesome toolkit for defining and managing http session (httr and rvest), declaring useragent string and investigating site policies (robotstxt), utilizing rate-limiting and reponse caching (ratelimitr amd memoise).

Installation

You can install the development version of polite from GitHub with:

# install.packages("devtools")
devtools::install_github("dmi3kno/polite")

Basic Example

This is a basic example which shows how to retrive the list of semi-soft cheeses from www.cheese.com. Here, we authenticate a session and then scrape the page with specified parameters. Behind the scenes polite retrieves robots.txt, checks the url and useragent string against it, caches the call to robots.txt and to the web page and enforces rate limiting.

library(polite)
library(rvest)
#> Loading required package: xml2

session <- bow("https://www.cheese.com/by_type", force = TRUE)
#> No encoding supplied: defaulting to UTF-8.
#> No encoding supplied: defaulting to UTF-8.
result <- scrape(session, params="t=semi-soft&per_page=100") %>%
  html_nodes("h3") %>% 
  html_text()
head(result)
#> [1] "3-Cheese Italian Blend"  "Abbaye de Citeaux"      
#> [3] "Abbaye du Mont des Cats" "Adelost"                
#> [5] "ADL Brick Cheese"        "Ailsa Craig"

Extended Example

You can build your own functions that incorporate bow, scrape (and, if required, nod). Here we will extend our inquiry into cheeses and will download all cheese names and url’s to their information pages. Lets retrieve number of pages per letter in the alphabetical list, keeping the number of results per page to 100 to minimize number of web requests.

library(polite)
library(rvest)
library(tidyverse)
#> -- Attaching packages ----------------------------------------------------------------------------------- tidyverse 1.2.1 --
#> v ggplot2 3.0.0     v purrr   0.2.5
#> v tibble  1.4.2     v dplyr   0.7.6
#> v tidyr   0.8.1     v stringr 1.3.1
#> v readr   1.1.1     v forcats 0.3.0
#> -- Conflicts -------------------------------------------------------------------------------------- tidyverse_conflicts() --
#> x dplyr::filter()         masks stats::filter()
#> x readr::guess_encoding() masks rvest::guess_encoding()
#> x dplyr::lag()            masks stats::lag()
#> x purrr::pluck()          masks rvest::pluck()

session <- bow("https://www.cheese.com/alphabetical")
#> No encoding supplied: defaulting to UTF-8.
#> No encoding supplied: defaulting to UTF-8.
responses <- map(letters, ~scrape(session, params = paste0("per_page=100&i=",.x)) )
results <- map(responses, ~html_nodes(.x, "#id_page") %>% 
                          html_text() %>% 
                          strsplit("\\s") %>% 
                          unlist() %>%
                          `%||%`(1) %>% 
                          as.numeric() %>% 
                          max(na.rm = TRUE) )
pages_df <- tibble(letter = rep.int(letters, times=unlist(results)),
                   pages = unlist(map(results, ~seq.int(from=1, to=.x))))
pages_df
#> # A tibble: 33 x 2
#>    letter pages
#>    <chr>  <int>
#>  1 a          1
#>  2 b          1
#>  3 b          2
#>  4 c          1
#>  5 c          2
#>  6 c          3
#>  7 d          1
#>  8 e          1
#>  9 f          1
#> 10 g          1
#> # ... with 23 more rows

Now that we know how many pages to retrieve from each letter page, lets rotate over letter pages and retrieve cheese names and underlying links to cheese details. We will need to write a helper function. Our session is still valid and we dont need to nod again, because we will not be modifying a page url, only its parameters (note that the field url is missing from scrape function).

get_cheese_page <- function(letter, pages){
 lnks <- scrape(session, params=paste0("per_page=100&i=",letter,"&page=",pages)) %>% 
    html_nodes("h3 a")
 tibble(name=lnks %>% html_text(),
        link=lnks %>% html_attr("href"))
}

df <- pages_df %>% pmap_df(get_cheese_page)
df
#> # A tibble: 1,830 x 2
#>    name                    link                     
#>    <chr>                   <chr>                    
#>  1 Abbaye de Belloc        /abbaye-de-belloc/       
#>  2 Abbaye de Belval        /abbaye-de-belval/       
#>  3 Abbaye de Citeaux       /abbaye-de-citeaux/      
#>  4 Abbaye de Timadeuc      /abbaye-de-timadeuc/     
#>  5 Abbaye du Mont des Cats /abbaye-du-mont-des-cats/
#>  6 Abbot’s Gold            /abbots-gold/            
#>  7 Abertam                 /abertam/                
#>  8 Abondance               /abondance/              
#>  9 Acapella                /acapella/               
#> 10 "Accasciato "           /accasciato/             
#> # ... with 1,820 more rows

Package logo is uses elements of free image by pngtree.com

[1] Wiktionary (2018), The free dictionary, retrieved from https://en.wiktionary.org/wiki/bow_and_scrape

You can’t perform that action at this time.