Circular shift of vector (equivalent to numpy.roll)

How about using head and tail...

roll <- function( x , n ){  if( n == 0 )    return( x )  c( tail(x,n) , head(x,-n) )}roll(1:5,2)#[1] 4 5 1 2 3#  For the situation where you supply 0 [ this would be kinda silly! :) ]roll(1:5,0)#[1] 1 2 3 4 5

One cool thing about using head and tail... you get a reverse roll with negative n, e.g.

roll(1:5,-2)[1] 3 4 5 1 2

Here's an alternative which has the advantage of working even when x is "rolled" by more than one full cycle (i.e. when abs(n) > length(x)):

roll <- function(x, n) {    x[(seq_along(x) - (n+1)) %% length(x) + 1]}roll(1:5, 2)# [1] 4 5 1 2 3roll(1:5, 0)# [1] 1 2 3 4 5roll(1:5, 11)# [1] 5 1 2 3 4

FWIW (and not that it's worth much) it also works on data.frames:

head(mtcars, 1)#           mpg cyl disp  hp drat   wt  qsec vs am gear carb# Mazda RX4  21   6  160 110  3.9 2.62 16.46  0  1    4    4head(roll(mtcars, 2), 1)#           gear carb mpg cyl disp  hp drat   wt  qsec vs am# Mazda RX4    4    4  21   6  160 110  3.9 2.62 16.46  0  1

The package binhf has the function shift:

library(binhf)shift(1:5, places = 2)#[1] 4 5 1 2 3

places can be positive or negative