[R] New line in caption with math symbols embedded in expression (paste(

[Izmirlian, Grant (NIH/NCI) [E]]

## I am using ggplot and trying to produce a caption containing math symbols. I need to
## add a second line. I did a fair amount of googling for answers. This one seemed like
## it would answer my question as it is nearly exactly my problem, except there is only
## one argument to the paste function. Note that my example is a complete minimal
## example, just a scatterplot with a line, and the caption content seems to not have
## anything to do with the plot. That is of course, intentional.
##
## https://stackoverflow.com/questions/13223846/ggplot2-two-line-label-with-expression

library(ggplot2)
X <- 10*runif(100)
Y <- 2*X + rnorm(100, sd=2)
fit <- lm(Y~X)
Y.p <- predict(fit, newdata=data.frame(X=X))
DAT <- data.frame(X=X)

## without a newline
p <- ggplot(data=DAT, aes(x=X)) + geom_point(aes(y=Y)) + geom_line(aes(y=Y.p))
p <- p + labs(caption=expression(paste(P,"(",FDP,">", alpha,") ",
                        "for 'FDR' and 'Auto' FDP control method, vs '", m,
                        "' at levels of 'eff size' (col) and '", p[1], "' (row)")))
p <- p + theme(plot.caption = element_text(hjust = 0))

## newline, method 1, just add a new component of paste containing "\n" somewhere in the middle
p <- ggplot(data=DAT, aes(x=X)) + geom_point(aes(y=Y)) + geom_line(aes(y=Y.p))
p <- p + labs(caption=expression(paste(P,"(",FDP,">", alpha,") ",
                        "for 'FDR' and 'Auto' FDP control method, vs '", m,
                        "' at levels of 'eff size' (col) and '", p[1], "' (row)",
                        "and \n a new line")))
p <- p + theme(plot.caption = element_text(hjust = 0))

## doesn't work because the newline affects only the last component of paste. It looks like new line
## works if the line is long enough, but the newline character is being parsed until the individual
## arguments to paste are parsed for math symbols but prior to pasting the components together. prior
## to pasting all arguments. I can't imagine why this would be the desired behavior. When the value of a
## caption argument is expression(paste(s1, s2, s3, ...)) then parsing for a newline character should
## occur after the components are pasted together, right?

## newline, method 2, enclose paste in another paste and add the new line as the second argument of the
## outer paste
p <- ggplot(data=DAT, aes(x=X)) + geom_point(aes(y=Y)) + geom_line(aes(y=Y.p))
p <- p + labs(caption=expression(paste(paste(P,"(",FDP,">", alpha,") ",
                        "for 'FDR' and 'Auto' FDP control method, vs '", m,
                        "' at levels of 'eff size' (col) and '", p[1], "' (row)"),
                        "and \n a new line")))
p <- p + theme(plot.caption = element_text(hjust = 0))

## which has the same behavior


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