############
#
# This file contains the code demonstrated in class.
#
# 1) It assumes you have a function descrip() that works appropriately on vectors,
#    including properly handling different storage modes (consider storage.mode() or
#    is.numeric(), is.character(), is.logical(), is.factor()):
#    a) vectors of characters (should it return NULL or count everything as missing?)
#    b) vectors of booleans (recall F=0, T=1 when coerced to numeric)
#    c) vectors of factors (these are coded as integers with labels applied when printing,
#       but what should you return?)
#    d) vectors of all missing data
#
# 2) I named the intermediate functions strdescr2(), strdescr3(), etc. You might want to use
#    more appropriate mnemonics if you take this general approach. Note that I did not
#    appropriately handle error in which, for instance, strdescr3() was called with
#    x a non-matrix
#
# 3) The handling of the default value for strata is far from optimal. You might consider
#    making the default value NULL in strdescr(...,strata) and using is.null() to generate the 
#    appropriate defaults in each of strdescr2() strdescr3() strdescr3a()
#
# 4) I put no error checks for the length of strata. You should handle it appropriately.
#
# 5) Rather than using the for() loops in strdescr3() and strdescr3a(), you could consider
#    using apply() and lapply(), respectively.
#
# 6) In strdescr(), you need to think about how you put variable names on your table when
#    a) the user supplies combinations of vectors and matrices or lists (data frames)
#    b) the user supplies only a single vector
#    c) the user supplies a matrix with no column names or a data frame with no names
# 
# 7) When calling strdescr() you will always have to supply the argument for strata in
#    order to distinguish it from one of the variables you want descriptives for (so
#    you might call strdescr(psadta[-9],M,strata=psadta$inrem))
#
# 8) Just to reiterate two points;
#    a) you need to carefully consider how your descrip() function acts with erroneous input
#    b) getting the row names in your output right will take some work
#
############

############
# Stratified statistics for a numeric vector: alternative versions for names
############

strdescr2 <- function (x,strata=rep(1,length(x))) {
	s <- sort(unique(strata))
	rslt <- rbind(All=descrip(x))
	if (length(s)>1){
		for (i in s) 
			rslt <- rbind(rslt,
				format(i)=descrip(x[strata==i]))
			}		
	rslt
	}

strdescr2 <- function (x,strata=rep(1,length(x))) {
	s <- sort(unique(strata))
	rslt <- descrip(x)
	if (length(s)>1){
		for (i in s) 
			rslt <- rbind(rslt,
				descrip(x[strata==i]))
			}		
	dimnames(rslt)[[1]]<- c("All",format(s))
	rslt
	}	

############
# Stratified statistics for a numeric matrix 
############

strdescr3 <- function (x,strata) {
	s <- sort(unique(strata))
	if (is.matrix(x)) {
		if (missing(strata)) strata <- rep(1,dim(x)[1])
		rslt <- NULL
		for (j in 1:dim(x)[2])
			rslt <- rbind(rslt,strdescr2(x[,j],strata))
	}
	rownames(rslt) <- paste(rep(colnames(x),each=length(s)+1),
			rownames(rslt))
	rslt
}

############
# Stratified statistics for a list of numeric vectors 
############

strdescr3a <- function (x,strata) {
	s <- sort(unique(strata))
	if (is.list(x)) {
		if (missing(strata)) strata <- rep(1,length(x[[1]]))
		rslt <- NULL
		for (j in 1:length(x))
			rslt <- rbind(rslt,strdescr2(x[[j]],strata))
	}
	rownames(rslt) <- paste(rep(names(x),each=length(s)+1),
			rownames(rslt))
	rslt
}

############
# Stratified statistics for an arbitrary combination of vectors, matrices, lists 
############

strdescr <- function (...,strata) {
	L <- list(...)
	names(L) <- as.vector(match.call(expand.dots=F)$...)
	if (missing(strata)) {
		if (is.vector(L[[1]])) strata=rep(1,length(L[[1]]))
		else if (is.matrix(L[[1]])) strata=rep(1,dim(L[[1]])[1])
		else strata=rep(1,length(L[[1]][[1]]))
		}
	# And now process L by making calls to strdescr2(), strdescr2(), strdescr3a()	rslt
}