lead-lag {dplyr} | R Documentation

## Lead and lag.

### Description

Find the "next" or "previous" values in a vector. Useful for comparing values ahead of or behind the current values.

### 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)

[Package dplyr version 0.7.0 Index]