how to add two regression line equations and R2s with each facet?

Question

I would like to add two regression line equations and R2s with each facet. I adopted Jayden's function to solve the problem, but I found that each equation was the same. The likely reason is sending wrong subset of data to the function. Any advice will be appreciated!

My code:

p <- ggplot(data=df,aes(x=x))+
  geom_point(aes(y = y1),size=2.0)+
  geom_smooth(aes(y = y1),method=lm,se=FALSE,size=0.5,
              fullrange = TRUE)+ # Add regression line;
  annotate("text",x = 150,y =320, label = lm_eqn(lm(y1~x,df)), # maybe wrong
           size = 2.0, parse = TRUE)+ # Add regression line equation;
  
  geom_point(aes(y = y2),size=2.0)+
  geom_smooth(aes(y = y2),method=lm,se=FALSE,size=0.5,
              fullrange = TRUE)+ # Add regression line;
  annotate("text",x = 225,y =50, label = lm_eqn(lm(y2~x,df)),
           size = 2.0, parse = TRUE)+ # Add regression line equation;
  facet_wrap(~trt)

My dataframe:

x   y1  y2  trt
22.48349    34.2    31.0    6030
93.52976    98.5    96.0    6030
163.00984   164.2   169.8   6030
205.62072   216.7   210.0   6030
265.46812   271.8   258.5   6030
23.79859    35.8    24.2    6060
99.97307    119.4   90.6    6060
189.91814   200.8   189.3   6060
268.10060   279.5   264.6   6060
325.65609   325.7   325.4   6060
357.59726   353.6   353.8   6060

My plot:

PS. There are two lines and your equations in each facet, and the two lines are right, but the two equations are wrong. Obviously, upper/lower equations in the right and left facet should be different to each other.

Answer 1

1) ggplot2 Try converting df to long form first (see ## line). We create an annotation data frame ann which defines the text and where it goes for use with geom_text. Note that since the plot is faceted by trt, geom_text will use the trt column in each row of ann to associate that row with the appropriate facet.

library(ggplot2)
library(reshape2)

long <- melt(df, measure.vars = 2:3) ##

trts <- unique(long$trt)
ann <- data.frame(x = c(0, 100), 
                  y = c(250, 100), 
                  label = c(lm_eqn(lm(y1 ~ x, df, subset = trt == trts[1])), 
                            lm_eqn(lm(y2 ~ x, df, subset = trt == trts[1])),
                            lm_eqn(lm(y1 ~ x, df, subset = trt == trts[2])), 
                            lm_eqn(lm(y2 ~ x, df, subset = trt == trts[2]))),
                  trt = rep(trts, each = 2),
                  variable = c("y1", "y2"))

ggplot(long, aes(x, value)) +
       geom_point() + 
       geom_smooth(aes(col = variable), method = "lm", se = FALSE,
              full_range = TRUE) + 
       geom_text(aes(x, y, label = label, col = variable), data = ann, 
             parse = TRUE, hjust = -0.1, size = 2) +
       facet_wrap(~ trt)

ann could equivalently be defined like this:

f <- function(v) lm_eqn(lm(value ~ x, long, subset = variable==v[[1]] & trt==v[[2]]))
Grid <- expand.grid(variable = c("y1", "y2"), trt = trts)
ann <- data.frame(x = c(0, 100), y = c(250, 100), label = apply(Grid, 1, f), Grid)

(continued after image)

2) lattice Its possibly easier in this case with lattice:

library(lattice)

xyplot(y1 + y2 ~ x | factor(trt), df, 
       key = simpleKey(text = c("y1", "y2"), col = c("blue", "red")),
       panel = panel.superpose, 
       panel.groups = function(x, y, group.value, ...) {
          if (group.value == "y1") {
              X <- 150; Y <- 300; col <- "blue"
          } else {
              X <- 250; Y <- 100; col <- "red"
          }
          panel.points(x, y, col = col)
          panel.abline(lm(y ~ x), col = col)
          panel.text(X, Y, parse(text = lm_eqn(lm(y ~ x))), col = col, cex = 0.7)
       }
)

(continued after image)

3) latticeExtra or we could make the lattice plot more ggplot2-like:

library(latticeExtra)

xyplot(y1 + y2 ~ x | factor(trt), df, par.settings = ggplot2like(),
       key = simpleKey(text = c("y1", "y2"), col = c("blue", "red")),
       panel = panel.superpose, 
       panel.groups = function(x, y, group.value, ...) {
          if (group.value == "y1") {
              X <- 150; Y <- 300; col <- "blue"
          } else {
              X <- 250; Y <- 100; col <- "red"
          }
          panel.points(x, y, col = col)
          panel.grid()
          panel.abline(lm(y ~ x), col = col)
          panel.text(X, Y, parse(text = lm_eqn(lm(y ~ x))), col = col, cex = 0.7)
       }
)

(continued after image)

Note: We used this as df:

df <-
structure(list(x = c(22.48349, 93.52976, 163.00984, 205.62072, 
265.46812, 23.79859, 99.97307, 189.91814, 268.1006, 325.65609, 
357.59726), y1 = c(34.2, 98.5, 164.2, 216.7, 271.8, 35.8, 119.4, 
200.8, 279.5, 325.7, 353.6), y2 = c(31, 96, 169.8, 210, 258.5, 
24.2, 90.6, 189.3, 264.6, 325.4, 353.8), trt = c(6030L, 6030L, 
6030L, 6030L, 6030L, 6060L, 6060L, 6060L, 6060L, 6060L, 6060L
)), .Names = c("x", "y1", "y2", "trt"), class = "data.frame", row.names = c(NA, 
-11L))

Update

• Added colored text.
• Added alternate ann.
• Added lattice solution.
• Added latticeExtra variation to the lattice solution.