I have a data frame which looks like this
aa bb
--------
a 1
a 2
a 3
b 4
b 5
b 1
I want above data frame to have a pair of elements picked from 'bb' and look like the below frame
aa bb cc
-------------
a 1 2
a 1 3
a 2 3
b 4 5
b 4 1
b 5 1
R input code
d1 <- read.table(header = TRUE, sep = ";", text =
"aa;bb
a;1
a;2
a;3
b;4
b;5
b;1" )
Using @Ananda Mahto's generous comments about the combn, we convert the 'data.frame' to 'data.table' (setDT(d1)), grouped by 'aa', we get the pairwise combinations of 'bb' (combn(bb,2)), extract the rows from it to create the 'bb' and 'cc'.
library(data.table)
setDT(d1)[,{tmp <- combn(bb,2)
list(bb= tmp[1,], cc= tmp[2,]) } , by = aa]
# aa bb cc
#1: a 1 2
#2: a 1 3
#3: a 2 3
#4: b 4 5
#5: b 4 1
#6: b 5 1
Using dplyr:
library(dplyr)
d1 %>% group_by(aa) %>%
do(data.frame(t(combn(.[["bb"]], 2))))
Source: local data frame [6 x 3]
Groups: aa [2]
aa X1 X2
(fctr) (dbl) (dbl)
1 a 1 2
2 a 1 3
3 a 2 3
4 b 4 5
5 b 4 1
6 b 5 1
Only base R.
d2 <- t(do.call(cbind, tapply(d1$bb, d1$aa, function(x)combn(x, 2))))
rownames(d2) <- d1$aa
d2
# [,1] [,2]
# a 1 2
# a 1 3
# a 2 3
# b 4 5
# b 4 1
# b 5 1
