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Based on the example here Adding Regression Line Equation and R2 on graph, I am struggling to include the regression line equation for my model in each facet. However, I don't figure why is changing the limits of my x axis.

library(ggplot2)
library(reshape2)

df <- data.frame(year = seq(1979,2010), M02 = runif(32,-4,6), 
M06 = runif(32, -2.4, 5.1), M07 = runif(32, -2, 7.1))
df <- melt(df, id = c("year"))


ggplot(data = df, mapping = aes(x = year, y = value)) +
geom_point() +
scale_x_continuous() + 
stat_smooth_func(geom = 'text', method = 'lm', hjust = 0, parse = T) +
geom_smooth(method = 'lm', se = T) +
facet_wrap(~ variable) # as you can see, the scale_x_axis goes back to 1800

If I include on the x the limits, 

scale_x_continuous(limits = c(1979,2010))

it does not show the regression coefficient anymore. What am I doing wrong here?

stat_smooth_func available here: https://gist.github.com/kdauria/524eade46135f6348140

Tung
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Andrei Niță
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2 Answers2

2

You can use stat_poly_eq function from the ggpmisc package.

library(reshape2)
library(ggplot2)
library(ggpmisc)
#> For news about 'ggpmisc', please, see https://www.r4photobiology.info/
#> For on-line documentation see https://docs.r4photobiology.info/ggpmisc/

df <- data.frame(year = seq(1979,2010), M02 = runif(32,-4,6), 
                 M06 = runif(32, -2.4, 5.1), M07 = runif(32, -2, 7.1))
df <- melt(df, id = c("year"))

formula1 <- y ~ x

ggplot(data = df, mapping = aes(x = year, y = value)) +
  geom_point() +
  scale_x_continuous() + 
  geom_smooth(method = 'lm', se = TRUE) +
  stat_poly_eq(aes(label = paste(..eq.label.., ..rr.label.., sep = "~~~~")), 
               label.x = "left", label.y = "top",
               formula = formula1, parse = TRUE, size = 3) +
  facet_wrap(~ variable) 


ggplot(data = df, mapping = aes(x = year, y = value)) +
  geom_point() +
  scale_x_continuous() + 
  geom_smooth(method = 'lm', se = TRUE) +
  stat_poly_eq(aes(label = paste(..eq.label.., sep = "~~~")), 
               label.x = "left", label.y = 0.15,
               eq.with.lhs = "italic(hat(y))~`=`~",
               eq.x.rhs = "~italic(x)",
               formula = formula1, parse = TRUE, size = 4) +
  stat_poly_eq(aes(label = paste(..rr.label.., sep = "~~~")), 
               label.x = "left", label.y = "bottom",
               formula = formula1, parse = TRUE, size = 4) +
  facet_wrap(~ variable)

Created on 2019-01-10 by the reprex package (v0.2.1.9000)

Tung
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    In case this is not obvious, using `expand_limits(y = 8)` for the upper example, or with a negative value for the second one, will avoid the overlap of the equations and the points. If the limits are not known in advance then the expansion can be set with `scale_y_continuous()`. – Pedro J. Aphalo May 13 '19 at 19:14
  • @PedroAphalo: thanks Pedro! Sometimes even if I specify `left` & `bottom`, the labels are still at the middle of the plot. Do you know what went wrong? https://i.imgur.com/J4ZNXMu.png – Tung May 17 '19 at 01:31
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Probably someone will suggest a better solution, but as an alternative, you can change stat_smooth_func and you can make the final row like this 

data.frame(x=1979, y=ypos, label=func_string)

instead of 

data.frame(x=xpos, y=ypos, label=func_string)

So, the plot will be like belowenter image description here

Senzeybek
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