Introduction
R has no separate Set datatype, instead using a variety of functions to perform similar operations on vectors.
The %in% operator tests for set membership.
2 %in% 1:10 # TRUE
12 %in% 1:10 # FALSE
Relevant functions include unique (to remove duplicates), plus union(), intersect(), setdiff() and setequal() to operate on pairs of sets.
> set_1 <- c("a", "b", "c", "b", "a")
> unique(set_1) # deduplicate
[1] "a" "b" "c"
> set_2 <- c('a', "c", "d")
> union(set_1, set_2) # values in either set
[1] "a" "b" "c" "d"
> intersect(set_1, set_2) # values in both sets
[1] "a" "c"
> setdiff(set_1, set_2) # values in set_1 but not set_2
[1] "b"
> setdiff(set_2, set_1) # values in set_2 but not set_1
[1] "d"
setequal(set_1, c("c", "b", "a", "b")) # are elements the same after deduplication?
[1] TRUE
In each case, set_1 and set_2 remain unchanged.
Instructions
Ozan is putting together a playlist for an upcoming roadtrip. He doesn"t want to hear the same track more than once, but the playlist has gotten so long that he"s having trouble remembering which tracks have already been added.
The API for Ozan"s music player only knows how to work with vectors. No explicit loops or if/else logic are possible. He needs your help!
1. Remove duplicate tracks
Implement the remove_duplicates function, which takes a playlist as a parameter and returns a new playlist where all the tracks are unique.
> playlist <- c(
"Court and Spark - Joni Mitchell",
"Big Yellow Taxi - Joni Mitchell",
"Court and Spark - Joni Mitchell"
)
> remove_duplicates(playlist)
[1] "Court and Spark - Joni Mitchell" "Big Yellow Taxi - Joni Mitchell"
2. Check whether a track has already been added
Implement the has_track function, which takes a playlist and a track as parameters and returns a boolean that indicates whether the playlist contains the track.
> playlist <- c(
"The Fashion Show - Grace Jones",
"Dr. Funkenstein - Parliament"
)
> has_track(playlist, "Dr. Funkenstein - Parliament")
[1] TRUE
> has_track(playlist, "Walking in the Rain - Grace Jones")
[1] FALSE
3. Add tracks
Implement the add_tracks function, which takes a playlist and a vector of one or more tracks as parameters and returns a new playlist that includes the tracks.
> playlist <- c("Selma - Bijelo Dugme")
> playlist <- add_tracks(playlist, "Atomic Dog - George Clinton")
> playlist
[1] "Selma - Bijelo Dugme" "Atomic Dog - George Clinton"
> add_tracks(playlist, "Selma - Bijelo Dugme")
[1] "Selma - Bijelo Dugme" "Atomic Dog - George Clinton"
> add_tracks(playlist, c("The Chain - Fleetwood Mac", "Selma - Bijelo Dugme"))
[1] "Selma - Bijelo Dugme" "Atomic Dog - George Clinton" "The Chain - Fleetwood Mac"
4. Delete tracks
Implement the delete_tracks function, which takes a playlist and one or more tracks as parameters and returns a new playlist that does not include the tracks.
> playlist <- c(
"The Treasure - Fra Lippo Lippi",
"After the Fall - Klaus Nomi"
)
> playlist <- delete_tracks(playlist, "The Treasure - Fra Lippo Lippi")
> playlist
[1] "After the Fall - Klaus Nomi"
> delete_tracks(playlist, "I Feel the Magic - Belinda Carlisle")
[1] "After the Fall - Klaus Nomi"
5. Compare playlists
Ozan meets a new friend and wonders how similar their tastes are.
Implement the find_common_tracks function, which takes two playlists and returns a new playlist containing only tracks present in both.
> playlist_1 <- c("Karma - Taylor Swift", "Tired - Adele")
> playlist_2 <- c("Andromeda - Weyes Blood", "Karma - Taylor Swift")
> find_common_tracks(playlist_1, playlist_2)
[1] "Karma - Taylor Swift"
Learning Exercise
