ggplot2 - Error using sapply and split to have different pvalues and r^2's on a facet wrap ggplot

I'm attempting to have different pvalues and r^2's show up on a plot I'm making using ggplot. My plot needs to be faceted, as I have many different factors of data I'm working on. The graphs I'm trying to make should all be linear models, but I'd like each to have it's own pvalue and r^2 show up in it's respective space.

I've been trying to use sapply to split the dataframe up and then calculate the r^2's and pvalues and then plug them back into the plot using geom_text(label = examplefunction), but I keep receiving the error "Error: Aesthetics must be either length 1 or the same as the data (244): x, y, label, hjust, vjust".

Here's an example using the "tips" dataframe from the reshape package:

library(reshape)


lm_equation <- function(tips){
  sapply(split(tips, list(tips$sex, tips$day)), function(tips){
    m <- lm(tips$tip ~ tips$total_bill, tips);
    eq <- substitute(~~italic(r)^2~"="~rvalue*","~italic(p)~"="~pvalue, 
                     list(rvalue = sprintf("%.2f",sign(coef(m)[2])*sqrt(summary(m)$r.squared)),
                          pvalue = format(summary(m)$coefficients[2,4], digits = 2)))
    as.character(as.expression(eq));
  })
}


scat <- ggplot(tips, aes(tip, total_bill))
scat +
  geom_point(size = 5, alpha = 0.9)+
  labs(x = "tip", y = "bill total")+
  geom_smooth(method=lm, colour = "#000000", se = F)+
  facet_grid(sex~day, scales = "free")+
  geom_text(x = min(tips$tip), y = max(tips$total_bill-10), label = lm_equation(tips), parse = T, vjust = "inward", hjust = "inward")+
  theme_classic() + 
  theme(text = element_text(size = 15))

What's frustrating is the code works if I take out the split, but then the pvalues and r^2s are meaningless since they are taken from the entire dataframe rather than just that specific faceted group.

Example of working code:

lm_equation2 <- function(tips){
    m <- lm(tips$tip ~ tips$total_bill, tips);
    eq <- substitute(~~italic(r)^2~"="~rvalue*","~italic(p)~"="~pvalue, 
                     list(rvalue = sprintf("%.2f",sign(coef(m)[2])*sqrt(summary(m)$r.squared)),

                          pvalue = format(summary(m)$coefficients[2,4], digits = 2)))
    as.character(as.expression(eq));
  }

scat2 <- ggplot(tips, aes(tip, total_bill))
scat2 +
  geom_point(size = 5, alpha = 0.9)+
  labs(x = "tip", y = "bill total")+
  geom_smooth(method=lm, colour = "#000000", se = F)+
  facet_grid(sex~day, scales = "free")+

  geom_text(x = min(tips$tip), y = max(tips$total_bill-10), label = lm_equation2(tips), parse = T, vjust = "inward", hjust = "inward")+
  theme_classic() + 
  theme(text = element_text(size = 15))

What am I missing here? Do I need to resort to subsetting my data?