ggplot2: Marimekko/Mosaic Chart

Another variation of the variable width column chart is a Marimekko chart or mosaic chart or eikosogram. In many marketing departments this chart is used to show proportion of a product market by region, and proportion of region by product. Jon Peltier’s tutorial demonstrates the technique to create one in Excel.

Let’s attempt to do the same in ggplot2.

We start with creating the dataframe to work with…

> df <- data.frame(segment = c("A", "B", "C", "D"), segpct = c(40, 30, 20, 10), Alpha = c(60, 40, 30, 25), Beta = c(25, 30, 30, 25), Gamma = c(10, 20, 20, 25), Delta = c(5, 10, 20, 25))

Next, I add a few helper variables, and convert the data to long format.

Calculate cumulative width on x-axes, starting point of each column and erase segpct variable.

> df$xmax <- cumsum(df$segpct) > df$xmin <- df$xmax - df$segpct > df$segpct <- NULL

Data looks like this before the long-format conversion:

> head(df) segment Alpha Beta Gamma Delta xmax xmin 1 A 60 25 10 5 40 0 2 B 40 30 20 10 70 40 3 C 30 30 20 20 90 70 4 D 25 25 25 25 100 90

After melting the data looks like this:

> library(ggplot2)

> dfm <- melt(df, id = c("segment", "xmin", "xmax")) > head(dfm) segment xmin xmax variable value 1 A 0 40 Alpha 60 2 B 40 70 Alpha 40 3 C 70 90 Alpha 30 4 D 90 100 Alpha 25 5 A 0 40 Beta 25 6 B 40 70 Beta 30

Now we need to determine how the columns are stacked and where to position the text labels.

Calculate ymin and ymax:

> dfm1 <- ddply(dfm, .(segment), transform, ymax = cumsum(value)) > dfm1 <- ddply(dfm1, .(segment), transform, ymin = ymax - value)

Positioning of text:

> dfm1$xtext <- with(dfm1, xmin + (xmax - xmin)/2) > dfm1$ytext <- with(dfm1, ymin + (ymax - ymin)/2)

Finally, we are ready to start the plotting process:

> p <- ggplot(dfm1, aes(ymin = ymin, ymax = ymax, xmin = xmin, xmax = xmax, fill = variable))

Use grey border to distinguish between the segments:

> p1 <- p + geom_rect(colour = I("grey"))

The explanation of different fill colours will be included in the text label of Segment A using the ifelse function.

> p2 <- p1 + geom_text(aes(x = xtext, y = ytext, label = ifelse(segment == "A", paste(variable, " - ", value, "%", sep = ""), paste(value, "%", sep = ""))), size = 3.5)

The maximum y-axes value is 100 (as in 100%), and to add the segment description above each column I manually specify the text position.

> p3 <- p2 + geom_text(aes(x = xtext, y = 103, label = paste("Seg ", segment)), size = 4)

Some last-minute changes to the default formatting: remove axis labels, legend and gridlines.

> p3 + theme_bw() + labs(x = NULL, y = NULL, fill = NULL) + opts(legend.position = "none", panel.grid.major = theme_line(colour = NA), panel.grid.minor = theme_line(colour = NA))

Or, if the default palette is not to one’s liking it is very easy to use a ColorBrewer palette instead:

> last_plot() + scale_fill_brewer(palette = "Set2")

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