| shift {quest} | R Documentation |
Shift a Vector (i.e., lag/lead)
Description
shift shifts elements of a vector right (n < 0) for lags or
left (n > 0) for leads replacing the undefined data with a
user-defined value (e.g., NA). The number of elements shifted is equal to
abs(n). It is assumed that x is already sorted by time such
that the first element is earliest in time and the last element is the latest
in time.
Usage
shift(x, n, undefined = NA)
Arguments
x |
atomic vector or list vector. |
n |
integer vector with length 1. Specifies the direction and magnitude of the shift. See details. |
undefined |
atomic vector with length 1 (probably makes sense to be the
same typeof as |
Details
If n is negative, then shift inserts undefined into the
first abs(n) elements of x, shifting all other values of
x to the right abs(n) positions, and then dropping the last
abs(n) elements of x to preserve the original length of
x. If n is positive, then shift drops the first
abs(n) elements of x, shifting all other values of x
left abs(n) positions, and then inserts undefined into the last
abs(n) elements of x to preserve the original length of
x. If n is zero, then shift simply returns x.
It is recommended to use L when specifying n to prevent
problems with floating point numbers. shift tries to circumvent this
issue by a call to round within shift if n is not an
integer; however that is not a complete fail safe. The problem is that
as.integer(n) implicit in shift truncates rather than rounds.
Value
an atomic vector of the same length as x that is shifted. If
x and undefined are different typeofs, then the return will
be coerced to the more complex typeof (i.e., complex to simple: character,
double, integer, logical).
See Also
Examples
shift(x = attitude[[1]], n = -1L) # use L to prevent problems with floating point numbers
shift(x = attitude[[1]], n = -2L) # can specify any integer up to the length of `x`
shift(x = attitude[[1]], n = +1L) # can specify negative or positive integers
shift(x = attitude[[1]], n = +2L, undefined = -999) # user-specified indefined value
shift(x = setNames(object = letters, nm = LETTERS), n = 3L) # names are kept