R programming: How can I compute the difference between two cells in a data frame and save them in a new column

Question

Trying to learn R and am stuck on an autocorrelation example. I want to regress the difference in x against the difference in y. I have x and y in a data frame, and would like the difference of x2 - x1 to be saved in a new column say dx. I have no idea how to go about this.

what I have:

data1

x   y
5   3
8   9
3   1
1   5
.   .
.   .
.   .

what I would like to get:

data1.dif

x   y   dx   dy
5   3   NA   NA
8   9    3    6
3   1   -5   -8
1   5   -2    4
.   .    .    .
.   .    .    .

Answer 1

Use diff with transform:

dat <- read.table(text="x   y
5   3
8   9
3   1
1   5", header=T)


transform(dat, dx=c(NA, diff(x)), dy=c(NA, diff(y)))

Yielding:

  x y dx dy
1 5 3 NA NA
2 8 9  3  6
3 3 1 -5 -8
4 1 5 -2  4

And as og dplyr:

library(dplyr)

dat %>%
    mutate(dx=c(NA, diff(x)), dy=c(NA, diff(y)))