J-League: Average Value vs. Average Age Plot

jleague_avg_value_age.r

# saw these types of plots for different leagues on r/soccer 
# (originally by Twitter: @fussbALEXperte) 
# so thought I'd make my own version using R!

library(rvest)
library(polite)
library(dplyr)
library(tidyr)
library(purrr)
library(ggplot2)
library(scales)
library(ggimage)
library(stringr)
library(glue)

url <- "https://www.transfermarkt.com/j-league-division-1/startseite/wettbewerb/JAP1/saison_id/2017"

session <- bow(url)

# grab team name from img instead...
team_name <- scrape(session) %>% 
  html_nodes("#yw1 > table > tbody > tr > td.zentriert.no-border-rechts > a > img") %>% 
  html_attr("alt")

# average age
avg_age <- scrape(session) %>% 
  html_nodes("tbody .hide-for-pad:nth-child(5)") %>% 
  html_text()

# average value
avg_value <- scrape(session) %>% 
  html_nodes("tbody .rechts+ .hide-for-pad") %>% 
  html_text()

# team image
team_img <- scrape(session) %>% 
  html_nodes("#yw1 > table > tbody > tr > td.zentriert.no-border-rechts > a > img") %>% 
  html_attr("src")
  
# combine above into one list
resultados <- list(team_name, avg_age, avg_value, team_img)

# specify column names
col_name <- c("team", "avg_age", "avg_value", "img")

# Combine into one dataframe
j_league_age_value_raw <- resultados %>% 
  reduce(cbind) %>% 
  as_data_frame() %>% 
  set_names(col_name)

# Clean up the values
j_league_age_value <- j_league_age_value_raw %>% 
  mutate(avg_age = avg_age %>% str_replace_all(",", ".") %>% as.numeric(),
         avg_value = avg_value %>% 
           str_replace_all("Th. \200", "000") %>% 
           str_replace(" ", "") %>% 
           as.numeric(),
         img = img %>% str_replace("/tiny/", "/head/")) %>% 
# Googled Euro-to-Yen exchange rate: 1 Euro = 129.39 Yen (8.25.18)
  mutate(avg_value = (avg_value * 129.39) %>% round(digits = 0),
         avg_value = avg_value / 10000) 

# Plot!
j_league_age_value %>% 
  ggplot(aes(x = avg_age, y = avg_value)) +
  geom_image(aes(image = img), size = 0.065) +
  scale_x_continuous(breaks = pretty_breaks(5),
                     limits = c(24, 29) ) +
  scale_y_continuous(labels = comma,
                   breaks = pretty_breaks(5)) +
  labs(title = "Jリーグ: 各チームの平均推定市場価格 vs. 平均年齢",
       subtitle = "",
       caption = "データ：transfermarkt.com",
       x = "平均年齢",
       y = "平均推定市場価格 (万円)") +
  theme_minimal() +
  theme(text = element_text(family = "IPAexGothic"))

ggsave(filename = "j_league_age_value_plot.png", height = 6, width = 8)