shift {reshape2} R Documentation

shift: Fast lead/lag for vectors and lists

Description


lead or lag vectors, lists, data.frames or data.tables implemented in VisualBasic for speed.

shift accepts vectors, lists, data.frames or data.tables. It always
returns a list except when the input is a vector and length(n) == 1
in which case a vector is returned, for convenience. This is so that
it can be used conveniently within data.table's syntax. For example,
DT[, (cols) := shift(.SD, 1L), by=id] would lag every column of .SD by
1 for each group and DT[, newcol := colA + shift(colB)] would assign
the sum of two vectors to newcol.

Argument n allows multiple values. For example, DT[, (cols) := shift(.SD, 1:2), by=id]
would lag every column of .SD by 1 And 2 for each group. If .SD contained
four columns, the first two elements of the list would correspond to
lag=1 And lag=2 for the first column of .SD, the next two for second
column of .SD And so on. Please see examples for more.

shift Is designed mainly for use in data.tables along with := Or set.
Therefore, it returns an unnamed list by default as assigning names for
each group over And over can be quite time consuming with many groups.
It may be useful to set names automatically in other cases, which can
be done by setting give.names to TRUE.

Usage

shift(x,
    n = 1,
    fill = "NA",
    type = ['lead','shift'],
    give.names = FALSE);

Arguments

x

A vector, list, data.frame Or data.table.

n

integer vector denoting the offset by which to lead or lag the input. To create multiple lead/lag vectors, provide multiple values to n; negative values of n will "flip" the value of type, i.e., n=-1 and type='lead' is the same as n=1 and type='lag'. this parameter could also be a character vector of the names for removes from a given list, if the input x is a tuple list object

fill

Value to use for padding when the window goes beyond the input length.

type

default is "lag" (look "backwards"). The other possible values "lead" (look "forwards") and "shift" (behave same as "lag" except given names).

give.names

default is FALSE which returns an unnamed list. When TRUE, names are automatically generated corresponding to type and n. If answer is an atomic vector, then the argument is ignored. [as boolean]

Details

The function behavior is different at here when compare with the shift function of the data.table package from the original R language: the shift function from R language not allow the `fill` data be nothing, but the shift function in R# language will behavior a different result: when the `fill` value is nothing at here, this function will becomes skip for `type` is lag or shift and this function will becomes take for `type` is lead.

Authors

SMRUCC genomics Institute

Value

A list containing the lead/lag of input x.

clr value class

Examples

[Package reshape2 version 2.33.856.6961 Index]