Histogram in R combining first two values

Question

I am drawing a histogram in R, and the first two frequencies are being combined into one bin which I do not want. There are seven possible values in the data and I would like 7 bins, not 6.

The info from the histogram drawn by R is,

$breaks
[1]  9 10 11 12 13 14 15

$counts
[1] 27  6  5  4  1 11

$density
[1] 0.50000000 0.11111111 0.09259259 0.07407407 0.01851852 0.20370370

$mids
[1]  9.5 10.5 11.5 12.5 13.5 14.5

$xname
[1] "data$hour"

$equidist
[1] TRUE

attr(,"class")
[1] "histogram"

The issue is in $counts, they should be:

9-20
10-7
11-6
12-5  
13-4
14-1
15-11

The data and command for histogram and info generation is:

temp <- c(9, 9, 9, 11, 12, 14, 15, 9, 9, 9, 10, 9, 13, 13, 15, 15, 9, 
9, 9, 11, 12, 13, 15, 15, 15, 9, 9, 10, 11, 12, 9, 10, 10, 12, 
15, 9, 9, 9, 9, 10, 11, 15, 9, 10, 10, 11, 11, 12, 13, 15, 15, 
9, 9, 15)

hist(temp)
histinfo = hist(temp)
histinfo

How can this be corrected? My thought is to count the occurrences and draw a barplot, but that seems like overkill since hist is already built in. I have tried changing breaks to no avail.

Thank you.

Answer 1

Use the table function with barplot

> barplot(table(temp))

Answer 2

When using hist you need breaks to bracket both ends if you want every single item. Therefore, the following will work.

hist(temp, breaks = 8:15)

If you don't like the 8 on the x-axis you'd have to suppress it and then draw the x-axis

hist(temp, breaks = 8:15, xaxt = 'n')
axis(1, 8:14+0.5, 9:15)

Unfortunately, the built in hist function should probably be used primarily for exploration and not publication so if you know that you called the function with arguments like right = TRUE then it should be clear to you what the output of the first graph means and easily interpreted (i.e. clearly there is nothing below 8).

Answer 3

You have to set breaks when drawing a histogram.

Personally, I would tabulate the data by hand and draw a barplot. Which may or may not be what you're really after.

library(reshape)
temp.melt <- melt(table(temp))

library(ggplot2)
ggplot(temp.melt, aes(x = temp, y = value)) +
  theme_bw() +
  geom_bar(stat = "identity")

Answer 4

Though this has been answered, I find this to be the simplest while also producing the best looking default chart:

library(ggplot2)
qplot( factor(temp) )

Answer 5

I contend this is a bug. Under the default arguments, the breakpoints are supposed to be right-closed, left open. Based on the documentation, for breaks=c(9, 10, 11, 12,13,14,15), breakpoints should be (9, 10], (10, 11], (11,12], (12,13], (13,14], (14,15]. Which would mean that the 9's wouldn't be plotted at all. It seems that hist is deciding that include.lowest=TRUE (despite the fact that argument is ignored unless you provide breaks a vector), so that the first interval is actually [9, 10].