Lag {Hmisc} | R Documentation

## Lag a Numeric, Character, or Factor Vector

### Description

Shifts a vector `shift` elements later. Character or factor variables are padded with `""`, numerics with `NA`.

### Usage

    Lag(x, shift = 1)

### Arguments

`x` | a vector
`shift` | positive integer specifying the number of observations to be shifted to the right

### Details

A.ttributes of the original object are carried along to the new lagged one, but factor vectors are converted to character.

### Value

a vector like `x`

### Author(s)

Frank Harrell

### See Also

`lag`

### Examples

    Lag(1:5,2)
    Lag(letters[1:4],2)
    Lag(factor(letters[1:4]),2)
    # Find which observations are the first for a given subject
    id <- c('a','a','b','b','b','c')
    id != Lag(id)
    !duplicated(id)

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