[R] Apply function to every 'nth' element of a vector

[ken knoblauch]

Michael Bach <phaebz <at> gmail.com> writes:
> how do I e.g. square each second element of a 
vector with an even
> number of elements? Or more generally to 
apply a function to every
> 'nth' element of a vector. I looked into the 
apply functions, but
> found no hint.
> For example:
> v <- c(1, 2, 3, 4)
> mysquare <- function (x) { return (x*x) }
> w <- applyfun(v, mysquare, 2)
> then w should be c(1, 4, 3, 16)
> Michael Bach

Hi Michael,

v^(2 - seq_along(v) %% 2)

[1]  1  4  3 16

Ken

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Ken Knoblauch
Inserm U846
Stem-cell and Brain Research Institute
Department of Integrative Neurosciences
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