Randomly Sample entries of a matrix and return the (Row, Column) Indexes in R? -


i have matrix m rows , n columns. need randomly sample different locations in these matrix , return row indexes , col indexes.

my approach: say, want sample 30 percentage of entries in matrix. then, iterate through whole matrix, @ each point, toss biased coin heads of 30 percent probability , select location if heads comes. since, data large, approximately selects 30% of entries. however, observe slow. there way speed up? or better way it?

if m matrix, try:

arrayind(sample(length(m),0.3*length(m)),dim(m))

an example:

set.seed(1) m<-matrix(ncol=6,nrow=6) arrayind(sample(length(m),0.3*length(m)),dim(m))       #     [,1] [,2] #[1,]    4    2 #[2,]    2    3 #[3,]    2    4 #[4,]    6    5 #[5,]    1    2 #[6,]    4    5 #[7,]    5    5 #[8,]    4    6 #[9,]    6    3 #[10,]    2    1

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