how to generate a graph/diagram like Google Analytics's Visitor Flow?

I thought this was an interesting question, so I made an example alluvial diagram using d3: http://nickrabinowitz.com/projects/d3/alluvial/alluvial.html

And, because d3 is so good at animation, and I thought it would look cool, I made an animated version as well: http://nickrabinowitz.com/projects/d3/alluvial/alluvial-dynamic.html

It doesn't cover everything you might want, but hopefully it will provide some basis. The large block of code in the beginning is just making fake data - you can replace this with your real data, or load it using d3.json. The expected format is similar to the DOM node structure d3 expects for network graphs:

{    // list of time slots t1 through tn    times: [        // list of t1 nodes        [            {                nodeName: "Node 1",                id: 1,                nodeValue: 24332            },            // etc ...        ],        // etc ...    ],    // list of all links    links: [        {            source: 1, // id of source node            target: 5, // id of target node            value: 3243        },        // ... etc    ]}

I hope that's helpful - this isn't a typical SO response, and it would likely require a certain amount of work to customize to your needs, but I thought it might be useful.

Consider Parallel coordinates plot in R

![Parallel Coordinate Plot of a Horse Race ][1]

df <- structure(list(Horse = structure(c(11L, 16L, 13L, 15L, 3L, 18L, 10L, 17L, 19L, 8L, 5L, 9L, 1L, 4L, 12L, 2L, 14L, 7L, 6L), .Label = c("Advice", "Atomic Rain", "Chocolate Candy", "Desert Party", "Dunkirk", "Flying Private", "Friesan Fire", "General Quarters", "Hold Me Back", "Join in the Dance", "Mine That Bird", "Mr. Hot Stuff", "Musket Man", "Nowhere to Hide", "Papa Clem", "Pioneer of the Nile", "Regal Ransom", "Summer Bird", "West Side Bernie"), class = "factor"), X1.4 = c(19L, 3L, 8L, 5L, 17L, 16L, 1L, 2L, 13L, 12L, 9L, 14L, 15L, 4L, 18L, 10L, 11L, 6L, 7L), X1.2 = c(19L, 3L, 8L, 4L, 12L, 16L, 1L, 2L, 17L, 13L, 10L, 5L, 15L, 6L, 18L, 9L, 14L, 7L, 11L), X3.4 = c(19L, 4L, 7L, 3L, 15L, 16L, 1L, 2L, 14L, 11L, 9L, 6L, 17L, 5L, 18L, 10L, 12L, 8L, 13L), X1m = c(12L, 2L, 7L, 4L, 8L, 15L, 1L, 3L, 17L, 10L, 11L, 5L, 13L, 6L, 16L, 9L, 18L, 14L, 19L), Str = c(1L, 2L, 4L, 3L, 7L, 9L, 5L, 6L, 13L, 10L, 12L, 8L, 14L, 11L, 16L, 15L, 18L, 17L, 19L), Finish = 1:19), .Names = c("Horse", "X1.4", "X1.2", "X3.4", "X1m", "Str", "Finish"), class = "data.frame", row.names = c(NA, -19L))library(ggplot2)df$Horse <- with(df, reorder(Horse, Finish))dfm <- melt(df)#add a volume metricdfm$volume <- ifelse(dfm$variable == "X1.4" & dfm$value <= 6,6,                ifelse(dfm$variable == "X1.4" & dfm$value > 6 & dfm$value <= 12,6,            ifelse(dfm$variable == "X1.4" & dfm$value > 12,7,1)))dfm$volume <- ifelse(dfm$variable == "X1.2" & dfm$value <= 9,9,                ifelse(dfm$variable == "X1.2" & dfm$value > 9 & dfm$value<= 14,5,            ifelse(dfm$variable == "X1.2" & dfm$value > 14,5,dfm$volume)))dfm$volume <- ifelse(dfm$variable == "X3.4" & dfm$value <= 3,3,                  ifelse(dfm$variable == "X3.4" & dfm$value > 3 & dfm$value <= 19,1,dfm$volume))#Alter the race for some neck to neck actiondfm$value <- ifelse(dfm$variable == "X1.4" & dfm$value <= 6,4,              ifelse(dfm$variable == "X1.4" & dfm$value > 6 & dfm$value <= 12,8,dfm$value))dfm$value <- ifelse(dfm$variable == "X1.2" & dfm$value <= 9,5,              ifelse(dfm$variable == "X1.2" & dfm$value > 9 & dfm$value <= 14,11,dfm$value))dfm$value <- ifelse(dfm$variable == "X3.4" & dfm$value <= 3,2,              ifelse(dfm$variable == "X3.4" & dfm$value > 3 & dfm$value <= 19,11,dfm$value))p <- ggplot(dfm, aes(factor(variable), value, group = Horse, colour = Horse, label = Horse))p1 <- p + geom_line(aes(size = volume), labels = labels) + geom_text(data = subset(dfm,variable == "Finish"), aes(x = factor(variable + 0.5)), size = 3.5, hjust = 0.8)labels <- c(expression(1/4), expression(1/2),expression(3/4), "1m", "Str", "Finish","")p1 + theme_bw() + opts(legend.position = "none",     panel.border = theme_blank(), axis.ticks = theme_blank()) +     scale_x_discrete(breaks = c(levels(dfm$variable),         ""), labels = labels) + scale_y_continuous(breaks = NA,     trans = "reverse") + xlab(NULL) + ylab(NULL)# Credit and other notes:# http://learnr.wordpress.com/2009/05/06/ggplot2-bump-chart/# ![enter image description here][1]http://had.co.nz/ggplot/plot-templates.html Parallel coordinates plot