Here is what I got for script through your third question:
set.seed(1) x1 = rbinom(200,1,.5) x2 = rbinom(200,1,.5) differ = x1 != x2 differ.indexes = (1:length(x1))[differ == TRUE] #you were unclear if you want to round up or round down on odd index of differ.indexes n = floor( length(differ.indexes)/2) #sampling without replacement random.indexes = sample(differ.indexes,n ) swapping = x1[random.indexes] #with 1s and 0s you can do this without this variable. x1[random.indexes] = x2[random.indexes] x2[random.indexes] = swapping Good luck, Jeremiah > Date: Tue, 17 Feb 2009 20:17:51 -0500 > From: esmail...@gmail.com > To: r-help@r-project.org > Subject: [R] how to randomly eliminate half the entries in a vector? > > Hello all, > > I need some help with a nice R-idiomatic and efficient solution to a > small problem. > > Essentially, I am trying to eliminate randomly half of the entries in > a vector that contains index values into some other vectors. > > > More details: > > I am working with two strings/vectors of 0s and 1s. These will contain > about 200 elements (always the same number for both) > > I want to: > > 1. determines the locations of where the two strings differ > > --> easy using xor(s1, s2) > > 2. *randomly* selects *half* of those positions > > --> not sure how to do this. I suppose the result would be > a list of index positions of size sum(xor(s1, s2))/2 > > > 3. exchange (flip) the bits in those random positions for both strings > > --> I have something that seems to do that, but it doesn't look > slick and I wonder how efficient it is. > > Mostly I need help for #2, but will happily accept suggestions for #3, > or for that matter anything that looks odd. > > Below my partial solution .. the HUX function is what I am trying > to finish if someone can point me in the right direction. > > Thanks > Esmail > ------ > > > > rm(list=ls()) > > #################################################### > # create a binary vector of size "len" > # > create_bin_Chromosome <- function(len) > { > sample(0:1, len, replace=T) > } > > > > #################################################### > # HUX - half uniform crossover > # > # 1. determines the locations of where the two strings > # differ (easy xor) > # > # 2. randomly selects half of those positions > # > # 3. exchanges (flips) the bits in those positions for > # both > # > HUX <- function(b1, b2) > { > # 1. find differing bits > r=xor(b1, b2) > > # positions where bits differ > different = which(r==TRUE) > > cat("\nhrp: ", different, "\n") > # 2. ??? how to do this best so that each time > # a different half subset is selected? I.e., > # sum(r)/2 positions. > > > # 3. this flips *all* positions, should really only flip > # half of them (randomly selected half) > new_b1 = b1 > new_b2 = b2 > > for(i in different) # should contain half the entries (randomly) > { > new_b1[i] = b2[i] > new_b2[i] = b1[i] > } > > result <- matrix(c(new_b1, new_b2), 2, LEN, byrow=T) > result > } > > > > LEN = 5 > b1=create_bin_Chromosome(LEN) > b2=create_bin_Chromosome(LEN) > > cat(b1, "\n") > cat(b2, "\n") > > idx=HUX(b1, b2) > cat("\n\n") > cat(idx[1,], "\n") > cat(idx[2,], "\n") > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. _________________________________________________________________ go. [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.