Stacked bar plot

Question

I have a data-frame whose first column is the name of an item and the second column is the frequency of that item in the dataset.

 names            freq
1 tomato           7
2 potato           4
3 cabbage          5
4 sukuma-wiki      8
5 terere           20

I would like to have a stacked bar column that depicts the proportion of each entry on the chart. How do you handle coloring of the stacked bar when presented with over sixty entries? what is the easiest way to do this?

Answer 1

With 60 distinct categories, I feel you may have a hard time making that an effective graphic. You may want to consider a regular bar-chart that is sorted in ascending or descending order. Whether or not these are counts or percentages is up to you. Maybe something like this:

library(ggplot2)
df$names <- reorder(df$names, -df$freq) #Reorders into ascending order
qplot(x = names, y = freq, data = df, geom = "bar") + coord_flip()

EDIT:

To make a stacked bar chart with ggplot, we set the x = 1 since we will have only one column. We will use the fill argument to add color:

qplot(x = factor(1), y = freq, data = df, geom = "bar", fill = names) 

Also of interest: a stacked bar chart is pretty darn close to being a pie chart. You can transform the coordinate system of ggplot charts with + coord_polar(theta = "y") to make a pie chart from the stacked bar chart above.

Answer 2

I doubt you fill find a suitable range of distinct colours with so much categories. Anyway, here are some ideas:

1. For stacked barchart, you need barplot() with beside=FALSE (which is the default) -- this is in base R (@Chase's solution with ggplot2 is good too)
2. For generating a color ramp, you can use the RColorBrewer package; the example shown by @fRed can be reproduced with brewer.pal and any one of the diverging or sequential palettes. However, the number of colour is limited, so you will need to recycle them (e.g., every 6 items)

Here is an illustration:

library(RColorBrewer)
x <- sample(LETTERS[1:20], 100, replace=TRUE)
tab <- as.matrix(table(x))
my.col <- brewer.pal(6, "BrBG") # or brewer.pal(6, "Blues")
barplot(tab, col=my.col)

There is also the colorspace package, which has a nice accompagnying vignette about the design of good color schemes. Check also Ross Ihaka's course on Topic in Computational Data Analysis and Graphics.

Now, a better way to display such data is probably to use a so-called Cleveland dot plot, i.e.

dotchart(tab)

Answer 3

For the coloring, either you specify a list of colors or you generate them.

In the latter, I suggest you execute this code

n = 32;
main.name = paste("color palettes; n=",n)
ch.col = c("rainbow(n, start=.7, end=.1)", "heat.colors(n)", "terrain.colors(n)",            "topo.colors(n)", "cm.colors(n)");

nt <- length(ch.col)
i <- 1:n; 
j <- n/nt; 
d <- j/6; 
dy <- 2*d;

plot(i,i+d, type="n", yaxt="n", xaxt="n", ylab="", , xlab ="", main=main.name)   #yaxt="n" set no y axie label and tick.
for (k in 1:nt) {
rect(i-.5, (k-1)*j+ dy, i+.4, k*j, col = eval(parse(text=ch.col[k])), border = "grey");
text(2.5*j, k * j + dy/2, ch.col[k])
}

taken from the blog http://statisticsr.blogspot.com/2008/07/color-scale-in-r.html

Barplotting should be done with ?barplot

DF=data.frame(names=c("tomato", "potato", "cabbage", "sukuma-wiki", "terere"), freq=c(7,4,5,8,20))
barplot(as.matrix(DF[,2]), col=heat.colors(length(DF[,2])), legend=DF[,1], xlim=c(0,9), width=2)