[R] random value changes in a vector

joris meys jorismeys at gmail.com
Tue Nov 18 23:21:44 CET 2008

The function rbinom might be a solution.

Try following simple program :
vec <- c(-1,1,-1,1,1,-1,-1,1,1)

inv <-rbinom(length(vec),1,0.5)
inv <-ifelse(inv==0,-1,1)

vec2 <- vec*inv  #switches sign with p=0.5

In this, inv is a random binomial vector, where the probability for
being 1 is 0.5 in all positions. Changing the values of 0 in this
vector to -1, gives you a vector you can multiply with the original
one to change the sign with a probability of 0.5 for all positions

Kind regards
On Tue, Nov 18, 2008 at 6:11 PM, Salas, Andria Kay <aks2515 at uncw.edu> wrote:
> To clear up a question regarding my earlier posting regarding random changes in a vector:
> Say you have a vector (1, -1, -1, 1, 1, -1).  I want each value in the vector to have a probability that it will change signs when this vector is regenerated.  For example, probability = 50%.  When the vector is regenerated, the first value in the vector (1) has a 50% chance of switching to -1.  If I regenerated this vector 10 times, 5 of the times it would switch to -1.  Similarly, I need each value in the vector to have this same probability of switching signs when the vector is regenerated, and each value's chances of doing so is independent of the other values.  So the second value (-1) also has a 50% chance of switching to 1, and whether or not it does so is independent of if the first value changes from 1 to -1 (also a 50% probability).
>  I hope this clears up the confusion, and I would appreciate any help anyone can provide!
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