dat <- data.frame(

• source = c('A', 'A', 'A', 'B', 'B', 'C'),
• target = c('B', 'C', 'D', 'C', 'D', 'D'),
• count = c(4, 5, 6, 3, 3, 5)
• )

names <- unique(c(dat$source, dat$target))

dat$source <- factor(dat$source, levels = names) dat$target <- factor(dat$target, levels = names)

mat <- xtabs(count ~ source + target, data = dat) mat[lower.tri(mat)] <- t(mat)[lower.tri(mat)] mat target source A B C D A 0 4 5 6 B 4 0 3 3 C 5 3 0 5 D 6 3 5 0