shift: Shift a vector an arbitrary amount
In geneorama/geneorama: Gene's collection of miscellaneous functions

Description Usage Arguments Note Author(s) Source Examples

Shift a variable by an amount, and pad with NA or your value of choice.

1	shift(x, offset = 1, pad = NA)

`x`	Vector to be shifted
`pad`	Value to use for padding
`shift`	Quantity to shift (forward or backward)

Can shift forward or backwards

Gene Leynes (originally dnlbrky http://stackoverflow.com/users/1344789/dnlbrky)

http://stackoverflow.com/questions/14689424/use-a-value-from-the-previous-row-in-an-r-data-table-calculation

		shift(1:10, 3)
     ## [1]  4  5  6  7  8  9 10 NA NA NA
	
		shift(1:10, -1)
     ## [1]  4  5  6  7  8  9 10 NA NA NA
     
     as.data.table(faithful)[1:5,list(eruptLengthCurrent=eruptions,
                                      eruptLengthTwoPrior=shift(eruptions,-2,0), 
      								 eruptLengthThreeFuture=shift(eruptions,3))]
     # eruptLengthCurrent eruptLengthTwoPrior eruptLengthThreeFuture
     # 1:              3.600               0.000                  2.283
     # 2:              1.800               0.000                  4.533
     # 3:              3.333               3.600                     NA
     # 4:              2.283               1.800                     NA
     # 5:              4.533               3.333                     NA
     
     shift(1:10, 3, NaN)
     # [1]   4   5   6   7   8   9  10 NaN NaN NaN