dplyr (version 0.5.0)

lead-lag: Lead and lag.

Description

Lead and lag are useful for comparing values offset by a constant (e.g. the previous or next value)

Usage

lead(x, n = 1L, default = NA, order_by = NULL, ...)
lag(x, n = 1L, default = NA, order_by = NULL, ...)

Arguments

x

a vector of values

n

a postive integer of length 1, giving the number of positions to lead or lag by

default

value used for non-existant rows. Defaults to NA.

order_by

override the default ordering to use another vector

...

Needed for compatibility with lag generic.

Examples

lead(1:10, 1)
lead(1:10, 2)

lag(1:10, 1)
lead(1:10, 1)

x <- runif(5)
cbind(ahead = lead(x), x, behind = lag(x))

# Use order_by if data not already ordered
df <- data.frame(year = 2000:2005, value = (0:5) ^ 2)
scrambled <- df[sample(nrow(df)), ]

wrong <- mutate(scrambled, prev = lag(value))
arrange(wrong, year)

right <- mutate(scrambled, prev = lag(value, order_by = year))
arrange(right, year)