Expected Points (xPts) for FantasyPL draft head-to-head league

fpl_xpts_draft_h2h.R

# Calculate expected points for a FantasyPL draft, head-to-head league.
# 
# Calculate expected points (xPts) and expected rank (xRank) for each
# team in a head-to-head draft league as the average points (i.e. 0, 1, 3)
# expected against all teams in that league each gameweek, not just the actual
# opponent.
# 
# @param leagueid: integer

library(dplyr)
library(data.table)
library(jsonlite)
library(glue)

xpts_draft_h2h <- function(leagueid) {
  fpl_json <- fromJSON(glue::glue("https://draft.premierleague.com/api/league/{leagueid}/details"))
  
  # get fixtures
  fixtures_df <- fpl_json$matches
  
  # get manager lookup
  manager_df <- fpl_json$league_entries %>% 
    select(id, name = entry_name)
  
  # get true head to head table
  table_df <- fpl_json$standings %>% 
    select(id=league_entry, pts=points_for, h2h_pts=total, rank=rank)
  
  # keep completed games only
  fixtures_df <- fixtures_df[fixtures_df$finished == 1,]
  
  scores_df <- rbind(
    fixtures_df %>% select(event, id = league_entry_1, pts = league_entry_1_points),
    fixtures_df %>% select(event, id = league_entry_2, pts = league_entry_2_points)
  )
  
  xpts_rounds <- lapply(unique(scores_df$event), function(i) {
    ss <- scores_df[scores_df$event == i,]
    lapply(unique(ss$id), function(j) {
      score <- ss[ss$id == j,]$pts
      opp_scores <- ss[ss$id != j,]$pts
      h2h_xpts <- (sum(as.numeric(score > opp_scores) * 3) + sum(as.numeric(score == opp_scores) * 1)) / length(opp_scores)
      data.frame(id = j, gw = i, pts = score, h2h_xpts)
    }) %>% 
      plyr::rbind.fill()
  }) %>% 
    plyr::rbind.fill()
  
  # table by expected points
  xpts_table <- xpts_rounds %>% 
    group_by(id) %>% 
    summarise(
      score = sum(pts),
      h2h_xpts = sum(h2h_xpts)) %>% 
    ungroup() %>% 
    arrange(-h2h_xpts)
  
  output_df <- left_join(
    table_df,
    xpts_table,
    on='id') %>% 
    left_join(manager_df, on = 'id') %>% 
    mutate(xrank = data.table::frank(., -h2h_xpts, score, -h2h_pts, ties.method='min')) %>% 
    arrange(xrank, name) %>% 
    select(rank, team=name, score, pts=h2h_pts, xPts=h2h_xpts, xRank=xrank)
  
  return(output_df)

}

# # example usage
# xpts_draft_h2h(81315)