Graphics Reference
In-Depth Information
It's possible to automatically extract values from the model object and build an expression using
those values. In this example, we'll create a string that, when parsed, returns a valid expression:
eqn
<-
as.character(as.expression(
substitute(italic(y)
==
a
+
b
*
italic(x)
*
","
~~ italic(r)
^
2
~
"="
~ r2,
list(a
=
format(coef(model)[
1
], digits
=
3
),
b
=
format(coef(model)[
2
], digits
=
3
),
r2
=
format(summary(model)$r.squared, digits
=
2
)
))))
eqn
"italic(y) == \"
37
.4
\
" + \"
1
.75
\
" * italic(x) * \"
,\
" ~ ~italic(r)^2 ~ \"
=
\
" ~
\"
0
.42
\
""
parse(text
=
eqn)
# Parsing turns it into an expression
expression(italic(y)
==
"37.4"
+
"1.75"
*
italic(x)
*
","
~ ~italic(r)
^
2
~
"="
~
"0.42"
)
Now that we have the expression string, we can add it to the plot. In this example we'll put the
text in the bottom-right corner, by setting
x=Inf
and
y=-Inf
and using horizontal and vertical
adjustments so that the text all fits inside the plotting area (
Figure 5-27
):
sp
+
annotate(
"text"
, label
=
eqn, parse
=
TRUE
TRUE
, x
=
Inf, y
=-
Inf, hjust
=
1.1
, vjust
=-
.5
)
