Graphics Reference
In-Depth Information
str(cabbage_exp)
'data.frame'
:
6
obs. of
6
variables:
$ Cultivar: Factor w
/
2
levels
"c39"
,
"c52"
:
1 1 1 2 2 2
$ Date : Factor w
/
3
levels
"d16"
,
"d20"
,
"d21"
:
1 2 3 1 2 3
$ Weight : num
3.18 2.8 2.74 2.26 3.11 1.47
$ sd : num
0.957 0.279 0.983 0.445 0.791 ...
$ n : int
10 10 10 10 10 10
$ se : num
0.3025 0.0882 0.311 0.1408 0.2501 ...
In the
mtcars
example,
cyl
is numeric, so it is treated as a continuous variable. Because of this,
even though the actual values of
cyl
include only 4, 6, and 8, the legend has entries for the inter-
mediate values 5 and 7. To make
ggplot()
treat
cyl
as a categorical variable, you can convert it
to a factor in the call to
ggplot()
, or you can modify the data so that the column is a character
vector or factor (
Figure 12-3
):
# Convert to factor in call to ggplot()
ggplot(mtcars, aes(x
=
wt, y
=
mpg, colour
=
factor(cyl)))
+
geom_point()
# Another method: Convert to factor in the data
m
<-
mtcars
# Make a copy of mtcars
m$cyl
<-
factor(m$cyl)
# Convert cyl to a factor
ggplot(m, aes(x
=
wt, y
=
mpg, colour
=
cyl))
+
geom_point()
