annotate a formula (with bqoute or substitute) in R (ggplot) gives Error

问题

I want to add a formula with variables in it as a annotation onto my ggplot.

regline1 <- 0.00
slope1 <- 1.00
dat <- as.data.frame(c(0,1))
dat[2] <- c(0,1)
names(dat) <- c("foo","bar")

p <-
ggplot(dat, aes(foo, bar)) + coord_fixed(ratio = 1) + geom_point()  + 
geom_abline(slope = slope1, intercept = intercept1, linetype = "dashed") +
labs(x =  substitute(y[H1]==i+s%*%x,list(i=format(intercept1, digits = 1), s= format(slope1, digits = 1))))

As you can see it is no problem for ggplot to evaluate the formula for labs(x =...), but if you try to add an annotation:

p +   annotate("text",x=0.75, y = 0.25, label = substitute(y[H1]==i+s%*%x,list(i=format(intercept1, digits = 1), s= format(slope1, digits = 1))))

it will give you an Error:

Error: Aesthetics must be either length 1 or the same as the data (1): label

I can parse a paste-call in annotate() like this:

p <- annotate("text",x= 0.75, y =0.25, label = "paste(y[H1]== intercept1+ slope1 %.%x)", parse = TRUE)

However, this does not write the variable values, since its in quotation marks. The substitute()-expression in quotation marks will not be parsed at all.

So how can I do this?

Any help is appreciated, thanks in advance Julius

回答1:

The annotate() function does not support expressions. you need to pass in a string and set parse=T.

If you first build your expression

myexpr <- substitute( y[H1]==i+s%*%x, list(
    i = format(intercept1, digits = 1), 
    s= format(slope1, digits = 1))
)

You can deparse() it and have annotate() re-parse it for you

ggplot(dat, aes(foo, bar)) + 
    geom_point()  + 
    geom_abline(slope = slope1, intercept = intercept1, linetype = "dashed") +
    coord_fixed(ratio = 1) + 
    labs(x = myexpr) + 
    annotate("text",x=0.75, y = 0.25, label = deparse(myexpr), parse=TRUE)

which results in

来源：https://stackoverflow.com/questions/43262808/annotate-a-formula-with-bqoute-or-substitute-in-r-ggplot-gives-error

标签

ggplot2

formula

annotate