Cars marker analytics

This small script helps to increase the experience of R, R-Shiny, JS and site scalping.

The idea comes when I looked for buying a car, but was struggling with the variety of cars in the market and was not certain whether or not the price was fair for a particular car. Since I have some data analysis background I decided to practice web scalping to make an analytical tool and visualize the Latvian market.

Make a famous site parser

We have an advertising site where people used to sell cars. So it has quite big data for analysis. These two libraries which analytics uses in R to parse sites:

• RSelenium

For the sake of simplicity, I decided to gather initial statistics with Rvest library. But initially, i played with Docker and RSelenium, so small instructions how to run RSelenium:

• install docker
• run it, restart the computer as requested
• pull image by running in command line: docker pull selenium/standalone-firefox(or chrome instead of firefox) or in R shell('docker pull selenium/standalone-firefox')
• start server by running in command line: docker run -d -p 4445:4444 selenium/standalone-firefox or in R shell('docker run -d -p 4445:4444 selenium/standalone-firefox')
• Then run remDr <- remoteDriver(remoteServerAddr = "localhost", port = 4445L, browserName = "firefox'")

So on localhost:4445 I managed to open the session and open a page of the site. I found it useful but not for my case, since I need just basic data which can be extracted much easier than with RSelenium

• RVest

I am quite familiar with this package so I used this instead. Small code which returns brands and the link is:

data_brands <- read_html("https://www.ss.com/lv/transport/cars/sell/filter/") %>%
   html_elements('.category') %>% {.[1:40]}
# make a dataframe with a link and the name of the brand
check_data <- data.frame(
        brand = data_brands %>% html_text2(),
        link = 
            paste0('https://www.ss.com/',data_brands %>% html_elements('a') %>% html_attr('href'))
        )

This code creates an initial data frame to use in a loop.

The next part is to make a parser:

total_data <- data.frame()
# for each brand I go through pages
for (brand in c(1:nrow(check_data))) {
  Sys.sleep(5)
  print(check_data$brand[brand])
  link <- check_data$link[brand]
  # randomly chosen page, if .navia class is not the same as the number of the page then break
  for (page in c(1:100)) {
    Sys.sleep(3)
    page_link <- paste0(link,"page",page,".html")
    print(page_link)
    navia_num <- read_html(page_link)
    page_num <- navia_num  %>%
      html_elements('.navia') %>% html_text2()
    # if there is only 1 page, then we set it to loop only first page.
    page_num <- ifelse(identical(page_num,character(0)), 1, page_num)
    
    if (page_num != page) {
      break
    } else {
      t_data <- navia_num %>%
        html_nodes(xpath = '//*[@id="filter_frm"]/table[2]') %>% 
        html_table() %>% 
        as.data.frame() %>%
        select(c(2:8)) %>%
        select(-1) %>%
        row_to_names(row_number=1) %>%
        slice(1:(n()-1)) %>%
        mutate(brand = check_data$brand[brand])
      
      total_data <- bind_rows(total_data, t_data)
      rm(t_data)
    }

  }
}

It will go to each car brand and take the list of cars. Since the site has pages and I cannot extract the total number per brand (not that easy with RVest, no problem with RSelenium though) I need that it will go to each page and once it reaches the last page it breaks if (page_num != page) {break}

So the log will be like this:

[1] "Chevrolet"
[1] "https://www.ss.com//lv/transport/cars/chevrolet/sell/page1.html"
[1] "https://www.ss.com//lv/transport/cars/chevrolet/sell/page2.html"
[1] "https://www.ss.com//lv/transport/cars/chevrolet/sell/page3.html"
[1] "https://www.ss.com//lv/transport/cars/chevrolet/sell/page4.html"
[1] "Chrysler"
[1] "https://www.ss.com//lv/transport/cars/chrysler/sell/page1.html"
[1] "https://www.ss.com//lv/transport/cars/chrysler/sell/page2.html"
[1] "https://www.ss.com//lv/transport/cars/chrysler/sell/page3.html"
[1] "https://www.ss.com//lv/transport/cars/chrysler/sell/page4.html"
[1] "https://www.ss.com//lv/transport/cars/chrysler/sell/page5.html"
[1] "https://www.ss.com//lv/transport/cars/chrysler/sell/page6.html"
[1] "https://www.ss.com//lv/transport/cars/chrysler/sell/page7.html"

at the end there will be an initial data frame:

So. With this data, we can work. And it is gonna be fun! We do create a new Shiny.App with the concept to analyse data which we parsed. I skip general info regarding Shiny application but will place some useful highlights.

How to connect Shiny with JS

How to send and receive data from JS

Instruction will be finished soon, while the actual deployment of the current application version is in:

https://ifarkhshatov.shinyapps.io/car_market_analysis