visualize associations between two groups of data

Question

Where each datapoint has a pairing of A and B and there multiple entries in A and multiple entires in B. IE multiple syndromes and multiple diagnoses, although for each data

Answer 1

This is what I do. A darker colour indicates a more important combination of A and B.

dataset <- data.frame(A = sample(LETTERS[1:5], 200, prob = runif(5), replace = TRUE), B = sample(LETTERS[1:5], 200, prob = runif(5), replace = TRUE))
Counts <- as.data.frame(with(dataset, table(A, B)))
library(ggplot2)
ggplot(Counts, aes(x = A, y = B, fill = Freq)) + geom_tile() + scale_fill_gradient(low = "white", high = "black")

Or if you prefer lines

library(ggplot2)
dataset <- data.frame(A = sample(letters[1:5], 200, prob = runif(5), replace = TRUE), B = sample(letters[1:5], 200, prob = runif(5), replace = TRUE))
Counts <- as.data.frame(with(dataset, table(A, B)))
Counts$X <- 0
Counts$Xend <- 1
Counts$Y <- as.numeric(Counts$A)
Counts$Yend <- as.numeric(Counts$B)
ggplot(Counts, aes(x = X, xend = Xend, y = Y, yend = Yend, size = Freq)) +
geom_segment() + scale_x_continuous(breaks = 0:1, labels = c("A", "B")) + 
scale_y_continuous(breaks = 1:5, labels = letters[1:5])

This third options add labels to the data points using geom_text().

library(ggplot2)
dataset <- data.frame(
    A = sample(letters[1:5], 200, prob = runif(5), replace = TRUE), 
    B = sample(LETTERS[20:26], 200, prob = runif(7), replace = TRUE)
)
Counts <- as.data.frame(with(dataset, table(A, B)))
Counts$X <- 0
Counts$Xend <- 1
Counts$Y <- as.numeric(Counts$A)
Counts$Yend <- as.numeric(Counts$B)
ggplot(Counts, aes(x = X, xend = Xend, y = Y, yend = Yend)) + 
geom_segment(aes(size = Freq)) + 
scale_x_continuous(breaks = 0:1, labels = c("A", "B")) + 
scale_y_continuous(breaks = -1) + 
geom_text(aes(x = X, y = Y, label = A), colour = "red", size = 7, hjust = 1, vjust = 1) + 
geom_text(aes(x = Xend, y = Yend, label = B), colour = "red", size = 7, hjust = 0, vjust = 0)