extract all the sub set of a set

sub_set

sub_index = function(x){
    n = length(x)
    com = paste0(rep('0:1,', n), collapse='')
    com = paste0('expand.grid(', 
                 substr(com, 1, nchar(com)-1),
                 ')', collapse = '')
    eval(parse(text = com))
}
sub_set = function(x){
    index = sub_index(x)
    apply(sub_index(x), 1, function(index) x[as.logical(index)])
}

x = 1:2
sub_set(x)