Question

I have a data frame consisting of the columns; “name”, “time”, “count”. Showing how many items took a given length of time. I would like to be able to draw a histogram based on the counts (and have hist() pick the boundaries etc.)

+------+------+-------+
| name | time | count |
+------+------+-------+
| foo  |    5 |     5 |
| foo  |   10 |     8 |
| foo  |   15 |     6 |
| foo  |   20 |     8 |
| bar  |    5 |     7 |
| bar  |   10 |     4 |
| bar  |   15 |     9 |
| bar  |   20 |    10 |
+------+------+-------+

From this I would like to be able to create histograms of times by name and times across the board. However, hist() counts up rows itself, I already have the counts in a count column. How can I achieve this?

Answer 1

The easiest is to use a barplot instead of a histogram.

library(lattice)
barchart( count ~ time | name, data=d )

library(ggplot2)
ggplot(d, aes(x=time, y=count)) + 
  geom_bar(stat="identity") + 
  facet_grid( ~ name )