I am trying to find difference in the first and last value of for a set of values in a given column in R. The example data table is
V1 V2
A 2
B 4
A 3
C 1
D 2
B 4
A 5
The output should take the first and last occurrence and give the result
V1 V2
A 3
B 0
C 1
D 2
I am confused as to which function to use to get to the result in r.
We can use aggregate from base R,
aggregate(V2 ~ V1, df, FUN = function(i) ifelse(length(i) > 1, tail(i, 1) - head(i, 1), i))
which gives,
V1 V2 1 A 3 2 B 0 3 C 1 4 D 2
DATA
dput(df)
structure(list(V1 = structure(c(1L, 2L, 1L, 3L, 4L, 2L, 1L), .Label = c("A",
"B", "C", "D"), class = "factor"), V2 = c(2L, 4L, 3L, 1L, 2L,
4L, 5L)), .Names = c("V1", "V2"), class = "data.frame", row.names = c(NA,
-7L))
We could use dplyr
library(dplyr)
df1 %>%
group_by(V1) %>%
summarise(V2 = if(n()>1) last(V2)- first(V2) else V2)
# A tibble: 4 x 2
# V1 V2
# <chr> <int>
#1 A 3
#2 B 0
#3 C 1
#4 D 2
