Get a histogram plot of factor frequencies (summary)

Question

I\'ve got a factor with many different values. If you execute summary(factor) the output is a list of the different values and their frequency. Like so:

Answer 1

Update in light of clarified Q

set.seed(1)
dat2 <- data.frame(fac = factor(sample(LETTERS, 100, replace = TRUE)))
hist(table(dat2), xlab = "Frequency of Level Occurrence", main = "")

gives:

Here we just apply hist() directly to the result of table(dat). table(dat) provides the frequencies per level of the factor and hist() produces the histogram of these data.

---

Original

There are several possibilities. Your data:

dat <- data.frame(fac = rep(LETTERS[1:4], times = c(3,3,1,5)))

Here are three, from column one, top to bottom:

• The default plot methods for class "table", plots the data and histogram-like bars
• A bar plot - which is probably what you meant by histogram. Notice the low ink-to-information ratio here
• A dot plot or dot chart; shows the same info as the other plots but uses far less ink per unit information. Preferred.

Code to produce them:

layout(matrix(1:4, ncol = 2))
plot(table(dat), main = "plot method for class \"table\"")
barplot(table(dat), main = "barplot")
tab <- as.numeric(table(dat))
names(tab) <- names(table(dat))
dotchart(tab, main = "dotchart or dotplot")
## or just this
## dotchart(table(dat))
## and ignore the warning
layout(1)

this produces:

If you just have your data in variable factor (bad name choice by the way) then table(factor) can be used rather than table(dat) or table(dat$fac) in my code examples.

For completeness, package lattice is more flexible when it comes to producing the dot plot as we can get the orientation you want:

require(lattice)
with(dat, dotplot(fac, horizontal = FALSE))

giving:

And a ggplot2 version:

require(ggplot2)
p <- ggplot(data.frame(Freq = tab, fac = names(tab)), aes(fac, Freq)) + 
    geom_point()
p

giving: