Esmail Bonakdarian
2009-Feb-18 03:13 UTC
[R] how to randomly eliminate half the entries in a vector?
(sorry if this is a duplicate-problems with posting at my end) ---- 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")
Gene Leynes
2009-Feb-18 03:22 UTC
[R] how to randomly eliminate half the entries in a vector?
This is my first help post, hope it works! Just check out the "sample" function At the command line type: ?sample I think it will be pretty clear from the documentation. On Tue, Feb 17, 2009 at 9:13 PM, Esmail Bonakdarian <esmail.js@gmail.com>wrote:> (sorry if this is a duplicate-problems with posting at my end) > ---- > 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. >[[alternative HTML version deleted]]
Esmail Bonakdarian
2009-Feb-18 03:33 UTC
[R] how to randomly eliminate half the entries in a vector?
Gene Leynes wrote:> This is my first help post, hope it works! > > Just check out the "sample" function > At the command line type: > ?sample > > I think it will be pretty clear from the documentation.Yes, most excellent suggestion and quite helpful! Thanks, Esmail