Compute Age and OPS for all players / seasons

batting_2000 <- batting_2000 |> 
  group_by(playerID, yearID) |>  # combine stints
  summarize(
    G = sum(G), AB = sum(AB), R = sum(R),
    H = sum(H), X2B = sum(X2B), X3B = sum(X3B),
    HR = sum(HR), RBI = sum(RBI), SB = sum(SB),
    CS = sum(CS), BB = sum(BB), SH = sum(SH),
    SF = sum(SF), HBP = sum(HBP),
    AB_career = first(AB_career),
    POS = first(POS)
  ) |>
  mutate(
    SLG = (H - X2B - X3B - HR + 2 * X2B + 3 * X3B + 4 * HR) / AB,
    OBP = (H + BB + HBP) / (AB + BB + HBP + SF),
    OPS = SLG + OBP
  ) |>      # add age
  inner_join(People, by = "playerID") |>
  mutate(
    Birthyear = if_else(
      birthMonth >= 7, birthYear + 1, birthYear
    ),
    Age = yearID - Birthyear
  ) |> 
  drop_na(Age)  # Drop NA's 

## `summarise()` has grouped output by 'playerID'. You can override using the
## `.groups` argument.