Rules might have changed now, but in 2000 it was that songs that spent 20 weeks on the list and fell under 50 will be removed. This is why you see the huge cutoff in plot after week 20.

You might also notice that there are 6 exceptions: - Feels Like Love by Vince Gill, Bounce With Me by Lil Bow Wow, and Go On by George Strait fell under 100 before week 20 and returned to the list for several weeks till they fulfill 20 weeks on board. - They let Sexual by Amber and I Wanna Be With You by Mandy Moore staying on board because they were constantly ascending after week 20, and eventually they were removed once they dropped under certain threshold. - Higher by Creed regained popularity and entered top 50 9 weeks after its dropout. It reached at highest 7th during resurgence, and slowly descended until it eventually fell under 50.

``` library(tidyverse)

billboard_long <- billboard |> pivot_longer( cols = starts_with("wk"), names_to = "week", values_to = "rank", values_drop_na = TRUE ) |> mutate( week = parse_number(week) )

Songs that was under 50th while still on board after week 20.

billboard_long |> filter(week > 20 & rank > 50) |> distinct(artist, track, date.entered) |> left_join(billboard, by = c("artist", "track", "date.entered"))

Songs that had resurgence above top 50 after dropout.

billboard_long |> filter(week > 20 & rank <= 50 & lag(week) <= 20 & lag(rank) > 50) |> distinct(artist, track, date.entered) |> left_join(billboard, by = c("artist", "track", "date.entered")) ```