Shifts a vector shift elements later. Character or factor variables are padded with "", numerics with NA. The shift may be negative.

Lag(x, shift = 1)

Arguments

x

a vector

shift

integer specifying the number of observations to be shifted to the right. Negative values imply shifts to the left.

Details

A.ttributes of the original object are carried along to the new lagged one.

Value

a vector like x

Author

Frank Harrell

See also

Examples

Lag(1:5,2)
#> [1] NA NA  1  2  3
Lag(letters[1:4],2)
#> [1] ""  ""  "a" "b"
Lag(factor(letters[1:4]),-2)
#> [1] c    d    <NA> <NA>
#> Levels: a b c d
# Find which observations are the first for a given subject
id <- c('a','a','b','b','b','c')
id != Lag(id)
#> [1]  TRUE FALSE  TRUE FALSE FALSE  TRUE
!duplicated(id)
#> [1]  TRUE FALSE  TRUE FALSE FALSE  TRUE