I am novice R programmer. I have this dummy data.frame.
a b group
1 4 1
5 5 1
7 8 1
10 9 1
14 0 2
18 4 2
20 5 2
25 7 2
29 10 3
35 15 3
40 22 3
48 44 3
57 34 4
68 65 4
77 8 4
86 55 4
I would like to produce the differences between groups 1 and 2, 2 and 3, 3 and 4 for columns a and b.
I think I am doing it very mechanically.
Thank you for your time
Here, the OP mentioned the 'group's have equal number of elements, So, one option is to remove the last 4 elements (head(df2, -4)[-3]) and first 4 elements (tail(df2, -4)[-3]) so that we will get the difference for columns 'a', 'b' between groups 1-2, 2-3, etc. as the 'group's are in order. For classification purpose, cbind with a 'group' vector created by pasteing the unique elements of 'group' (by removing the 1st and last element)
un1 <- unique(df2$group)
cbind(group = rep(paste(un1[-length(un1)], un1[-1], sep="-"), each = 4),
head(df2,-4)[-3]- tail(df2,-4)[-3])
# group a b
#1 1-2 -13 4
#2 1-2 -13 1
#3 1-2 -13 3
#4 1-2 -15 2
#5 2-3 -15 -10
#6 2-3 -17 -11
#7 2-3 -20 -17
#8 2-3 -23 -37
#9 3-4 -28 -24
#10 3-4 -33 -50
#11 3-4 -37 14
#12 3-4 -38 -11