Graphics Reference
In-Depth Information
tg
supp dose length
OJ
0.5 13.23
OJ
1.0 22.70
OJ
2.0 26.06
VC
0.5 7.98
VC
1.0 16.77
VC
2.0 26.14
str(tg)
'data.frame'
:
6
obs. of
3
variables:
$ supp : Factor w
/
2
levels
"OJ"
,
"VC"
:
1 1 1 2 2 2
$ dose : num
0.5 1 2 0.5 1 2
$ length: num
13.23 22.7 26.06 7.98 16.77 ...
NOTE
If the xvariable is a factor, you must also tell
ggplot()
to
group
by that same variable, as described
momentarily.
Line graphs can be used with a continuous or categorical variable on the x-axis. Sometimes the
variable mapped to the x-axis is conceivedof as being categorical, even when it's stored as a
number. In the example here, there are three values of
dose
: 0.5, 1.0, and 2.0. You may want to
treat these as categories rather than values on a continuous scale. To do this, convert
dose
to a
factor (
Figure 4-7
):
ggplot(tg, aes(x
=
factor(dose), y
=
length, colour
=
supp, group
=
supp))
+
geom_line()
