This post has referred to a vignette from dplyr, you can
find it in https://dplyr.tidyverse.org/articles/two-table.html.
We’ll try to display how to join data tables in this vignette. First,
load the packages we need and get some data.
library(tidyfst)
library(nycflights13)
flights2 <- flights %>%
select_dt(year,month,day, hour, origin, dest, tailnum, carrier)Do a left join with a simple:
flights2 %>%
left_join_dt(airlines)
#> Joining by: carrier
#> Key: <carrier>
#> carrier year month day hour origin dest tailnum
#> <char> <int> <int> <int> <num> <char> <char> <char>
#> 1: 9E 2013 1 1 8 JFK MSP N915XJ
#> 2: 9E 2013 1 1 15 JFK IAD N8444F
#> 3: 9E 2013 1 1 14 JFK BUF N920XJ
#> 4: 9E 2013 1 1 15 JFK SYR N8409N
#> 5: 9E 2013 1 1 15 JFK ROC N8631E
#> ---
#> 336772: YV 2013 9 29 16 LGA IAD N518LR
#> 336773: YV 2013 9 29 17 LGA CLT N932LR
#> 336774: YV 2013 9 30 16 LGA IAD N510MJ
#> 336775: YV 2013 9 30 17 LGA CLT N905FJ
#> 336776: YV 2013 9 30 20 LGA CLT N924FJ
#> 1 variable not shown: [name <char>]Join works the same as dplyr:
flights2 %>% left_join_dt(weather)
#> Joining by: year,month,day,hour,origin
#> Key: <year, month, day, hour, origin>
#> year month day hour origin dest tailnum carrier temp dewp
#> <int> <int> <int> <int> <char> <char> <char> <char> <num> <num>
#> 1: 2013 1 1 5 EWR IAH N14228 UA 39.02 28.04
#> 2: 2013 1 1 5 EWR ORD N39463 UA 39.02 28.04
#> 3: 2013 1 1 5 JFK MIA N619AA AA 39.02 26.96
#> 4: 2013 1 1 5 JFK BQN N804JB B6 39.02 26.96
#> 5: 2013 1 1 5 JFK BOS N708JB B6 39.02 26.96
#> ---
#> 336772: 2013 12 31 23 EWR SJU N651JB B6 NA NA
#> 336773: 2013 12 31 23 JFK BQN N566JB B6 NA NA
#> 336774: 2013 12 31 23 JFK SJU N713TW DL NA NA
#> 336775: 2013 12 31 23 JFK SJU N509JB B6 NA NA
#> 336776: 2013 12 31 23 JFK PSE N665JB B6 NA NA
#> 8 variables not shown: [humid <num>, wind_dir <num>, wind_speed <num>, wind_gust <num>, precip <num>, pressure <num>, visib <num>, time_hour <POSc>]
flights2 %>% left_join_dt(planes, by = "tailnum")
#> Key: <tailnum>
#> tailnum year.x month day hour origin dest carrier year.y type
#> <char> <int> <int> <int> <num> <char> <char> <char> <int> <char>
#> 1: <NA> 2013 1 2 15 JFK LAX AA NA <NA>
#> 2: <NA> 2013 1 2 16 EWR ORD UA NA <NA>
#> 3: <NA> 2013 1 3 8 EWR MIA UA NA <NA>
#> 4: <NA> 2013 1 3 6 EWR DFW UA NA <NA>
#> 5: <NA> 2013 1 4 8 JFK DCA 9E NA <NA>
#> ---
#> 336772: N9EAMQ 2013 9 27 16 LGA ATL MQ NA <NA>
#> 336773: N9EAMQ 2013 9 29 12 LGA BNA MQ NA <NA>
#> 336774: N9EAMQ 2013 9 29 18 LGA CMH MQ NA <NA>
#> 336775: N9EAMQ 2013 9 30 11 JFK DCA MQ NA <NA>
#> 336776: N9EAMQ 2013 9 30 14 JFK TPA MQ NA <NA>
#> 6 variables not shown: [manufacturer <char>, model <char>, engines <int>, seats <int>, speed <int>, engine <char>]
flights2 %>% left_join_dt(airports, c("dest" = "faa"))
#> Key: <dest>
#> dest year month day hour origin tailnum carrier
#> <char> <int> <int> <int> <num> <char> <char> <char>
#> 1: ABQ 2013 10 1 20 JFK N554JB B6
#> 2: ABQ 2013 10 2 20 JFK N607JB B6
#> 3: ABQ 2013 10 3 20 JFK N591JB B6
#> 4: ABQ 2013 10 4 20 JFK N662JB B6
#> 5: ABQ 2013 10 5 19 JFK N580JB B6
#> ---
#> 336772: XNA 2013 9 29 17 LGA N725MQ MQ
#> 336773: XNA 2013 9 30 7 LGA N735MQ MQ
#> 336774: XNA 2013 9 30 8 EWR N14117 EV
#> 336775: XNA 2013 9 30 15 LGA N725MQ MQ
#> 336776: XNA 2013 9 30 17 LGA N720MQ MQ
#> 7 variables not shown: [name <char>, lat <num>, lon <num>, alt <num>, tz <num>, dst <char>, tzone <char>]
flights2 %>% left_join_dt(airports, c("origin" = "faa"))
#> Key: <origin>
#> origin year month day hour dest tailnum carrier
#> <char> <int> <int> <int> <num> <char> <char> <char>
#> 1: EWR 2013 1 1 5 IAH N14228 UA
#> 2: EWR 2013 1 1 5 ORD N39463 UA
#> 3: EWR 2013 1 1 6 FLL N516JB B6
#> 4: EWR 2013 1 1 6 SFO N53441 UA
#> 5: EWR 2013 1 1 6 LAS N76515 UA
#> ---
#> 336772: LGA 2013 9 30 18 BNA N740EV EV
#> 336773: LGA 2013 9 30 22 SYR <NA> 9E
#> 336774: LGA 2013 9 30 12 BNA N535MQ MQ
#> 336775: LGA 2013 9 30 11 CLE N511MQ MQ
#> 336776: LGA 2013 9 30 8 RDU N839MQ MQ
#> 7 variables not shown: [name <char>, lat <num>, lon <num>, alt <num>, tz <num>, dst <char>, tzone <char>]df1 <- data.table(x = c(1, 2), y = 2:1)
df2 <- data.table(x = c(1, 3), a = 10, b = "a")
df1 %>% inner_join_dt(df2)
#> Joining by: x
#> Key: <x>
#> x y a b
#> <num> <int> <num> <char>
#> 1: 1 2 10 a
df1 %>% left_join_dt(df2)
#> Joining by: x
#> Key: <x>
#> x y a b
#> <num> <int> <num> <char>
#> 1: 1 2 10 a
#> 2: 2 1 NA <NA>
df1 %>% right_join_dt(df2)
#> Joining by: x
#> Key: <x>
#> x y a b
#> <num> <int> <num> <char>
#> 1: 1 2 10 a
#> 2: 3 NA 10 a
df1 %>% full_join_dt(df2)
#> Joining by: x
#> Key: <x>
#> x y a b
#> <num> <int> <num> <char>
#> 1: 1 2 10 a
#> 2: 2 1 NA <NA>
#> 3: 3 NA 10 aIf all you have is a data.frame or tibble, you have no need to change the format. Feed the data directly:
df1 <- data.frame(x = c(1, 1, 2), y = 1:3)
df2 <- data.frame(x = c(1, 1, 2), z = c("a", "b", "a"))
df1 %>% left_join_dt(df2)
#> Joining by: x
#> Key: <x>
#> x y z
#> <num> <int> <char>
#> 1: 1 1 a
#> 2: 1 1 b
#> 3: 1 2 a
#> 4: 1 2 b
#> 5: 2 3 aThe “_dt” suffix should remind you that this is backed up by
data.table and will always return a data.table in the
end.
Filtering joins have also been supported in tidyfst.
flights %>%
anti_join_dt(planes, by = "tailnum") %>%
count_dt(tailnum, sort = TRUE)
#> tailnum n
#> <char> <int>
#> 1: <NA> 2512
#> 2: N725MQ 575
#> 3: N722MQ 513
#> 4: N723MQ 507
#> 5: N713MQ 483
#> ---
#> 718: N7BKAA 1
#> 719: N7CAAA 1
#> 720: N5FCAA 1
#> 721: N5ERAA 1
#> 722: N647MQ 1Other examples (semi_join_dt() and
anti_join_dt() never duplicate; they only ever remove
observations.):
df1 <- data.frame(x = c(1, 1, 3, 4), y = 1:4)
df2 <- data.frame(x = c(1, 1, 2), z = c("a", "b", "a"))
# Four rows to start with:
df1 %>% nrow()
#> [1] 4
# And we get four rows after the join
df1 %>% inner_join_dt(df2, by = "x") %>% nrow()
#> [1] 4
# But only two rows actually match
df1 %>% semi_join_dt(df2, by = "x") %>% nrow()
#> [1] 2For set operations, wrap data.table’s function directly,
but the functions will automatically turn any data.frame into
data.table. Examples are listed as below:
x = iris[c(2,3,3,4),]
x2 = iris[2:4,]
y = iris[c(3:5),]
intersect_dt(x, y) # intersect
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> <num> <num> <num> <num> <fctr>
#> 1: 4.7 3.2 1.3 0.2 setosa
#> 2: 4.6 3.1 1.5 0.2 setosa
intersect_dt(x, y, all=TRUE) # intersect all
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> <num> <num> <num> <num> <fctr>
#> 1: 4.7 3.2 1.3 0.2 setosa
#> 2: 4.6 3.1 1.5 0.2 setosa
setdiff_dt(x, y) # except
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> <num> <num> <num> <num> <fctr>
#> 1: 4.9 3 1.4 0.2 setosa
setdiff_dt(x, y, all=TRUE) # except all
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> <num> <num> <num> <num> <fctr>
#> 1: 4.9 3.0 1.4 0.2 setosa
#> 2: 4.7 3.2 1.3 0.2 setosa
union_dt(x, y) # union
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> <num> <num> <num> <num> <fctr>
#> 1: 4.9 3.0 1.4 0.2 setosa
#> 2: 4.7 3.2 1.3 0.2 setosa
#> 3: 4.6 3.1 1.5 0.2 setosa
#> 4: 5.0 3.6 1.4 0.2 setosa
union_dt(x, y, all=TRUE) # union all
#> Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> <num> <num> <num> <num> <fctr>
#> 1: 4.9 3.0 1.4 0.2 setosa
#> 2: 4.7 3.2 1.3 0.2 setosa
#> 3: 4.7 3.2 1.3 0.2 setosa
#> 4: 4.6 3.1 1.5 0.2 setosa
#> 5: 4.7 3.2 1.3 0.2 setosa
#> 6: 4.6 3.1 1.5 0.2 setosa
#> 7: 5.0 3.6 1.4 0.2 setosa
setequal_dt(x, x2, all=FALSE) # setequal
#> [1] TRUE
setequal_dt(x, x2)
#> [1] FALSEFor more details, just find the help from data.table
using ?setops.