Convert 2 by 2 Contingency Table to Data Frame in R

Contingency tables are useful short hand ways of inputting and visualizing data. I have yet to find an easy way to convert between contingency tables and data frames in R. Below is a short script in which I input a contingency table, create a function to convert the 2 by 2 table to a data frame, and convert the data frame back to a table. These operations are useful for running some statistical operations that either only work on tables or only work on data frames. Hope the below example is useful.

	# Input Contingency Table Data
	a=371 # Exposed Case
	b=62 # Non-exposed Case
	c=85 # Exposed Control
	d=18 # Non-exposed Control
	tbl <- matrix(c(a, c, b, d), nrow = 2,
	dimnames=list(Case=c("Case", "Control"),
	Exposed=c("Exposed", "Unexposed")))
	tbl
	# Function to Convert Table to Data Frame
	tbl_df <- function(tbl)
	{
	rows <- c(rep(row.names(tbl)[1],sum(tbl[1,])),rep(row.names(tbl)[2],sum(tbl[2,])))
	cols <- c(rep(colnames(tbl)[1],sum(tbl[1,1])),rep(colnames(tbl)[2],sum(tbl[1,2])),
	rep(colnames(tbl)[1],sum(tbl[2,1])),rep(colnames(tbl)[2],sum(tbl[2,2])))
	out <- data.frame(rows,cols)
	names(out) <- names(dimnames(tbl))
	return(out)
	}
	# Run Function and Save Output
	out <- tbl_df(tbl)
	# Confirm Function
	head(out)
	tbl2 <- table(out$Case,out$Exposed)
	tbl2
	tbl2 == tbl
	# Example Statistical Tests
	r <- cor(as.numeric(out$Case)-1,as.numeric(out$Exposed)-1)
	r**2
	chisq.test(tbl, correct=F)

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