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I have a vector:
a <- c(1,2,3,4,5) And I'd like to do something like:
b <- roll(a, 2) # 4,5,1,2,3 Is there a function like that in R? I've been googling around, but "R Roll" mostly gives me pages about Spanish pronunciation.
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Using Collection deque This method allows us to shift by n elements ahead at once, using both directions, forward and backward. We just need to use the rotate method on the deque object. Note, that you can easily convert a deque object to a list like list(x) where x is a deque object.
To shift the bits of integer array elements to the right, use the numpy. right_shift() method in Python Numpy. Bits are shifted to the right x2. Because the internal representation of numbers is in binary format, this operation is equivalent to dividing x1 by 2**x2.
Shift Array in Python Using the numpy.roll(array, shift, axis) method takes the array as input and rotates it to the positions equal to the shift value. If the array is a two-dimensional array, we will need to specify on which axis we need to apply the rotation; otherwise, the numpy.
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 3 roll(1:5, 0) # [1] 1 2 3 4 5 roll(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 4 head(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 If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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