Graphics Reference
In-Depth Information
Figure 5-26. Left: plain text; right: math expression
Instead of using a plain text string, it's also possible to enter formulas using R's math expression
syntax, by setting
parse=TRUE
:
sp
+
annotate(
"text"
, label
=
"r^2 == 0.42"
, parse
=
TRUE
TRUE
, x
=
16.5
, y
=
52
)
Discussion
Text geoms in ggplot2 do not take expression objects directly; instead, they take character strings
that are turned into expressions with
parse(text="a + b")
.
If you use a math expression, the syntax must be correct for it to be a valid R expression object.
You can test validity by wrapping it in
expression()
and seeing if it throws an error (make
sure notto use quotes around the expression). In the example here,
==
is a valid construct in an
expression to express equality, but
=
is not:
expression(r
^
2
==
0.42
)
# Valid
expression(r
^
2
==
0.42
)
expression(r
^
2
=
0.42
)
# Not valid
Error: unexpected
'='
in
"expression(r^2 ="
