build.position.index.R

build.position.index = function(x, by = 5) {
	
	segment = round((x/(10^by)))*10^by 
	se = unique(segment)
	mat = matrix(nrow = length(se), ncol = 2)
	for(i in seq_along(se)) {
		mat[i, ] = range(which(segment == se[i]))
	}
	list(mat = mat, segment = se, by = 10^by)
}

get.position.index = function(x, index) {
	i = round(x / index$by)
	index$mat[i+1, ]
}