Extend geom_smooth in a single direction

Allows to extend a linear regression line drawn with ggplot2::geom_smooth() to only one direction (left or right), or to zero. DOES NOT WORK WITH CURRENT VERSION OF GGPLOT2. You have to include source("https://raw.githubusercontent.com/larmarange/JLutils/master/R/lm_right.R") into your R code.

lm_right(formula, data, ...)

lm_left(formula, data, ...)

lm_zero(formula, data, ...)

Arguments

formula

a model formula

data

a data.frame

...

unused

Details

cf. https://github.com/tidyverse/ggplot2/issues/3132 The implementation should be through a new stat rather than extending predictdf()

Note: xseq could be passed to ggplot2::geom_smooth()

Note

Adapted from https://stackoverflow.com/questions/26705554/extend-geom-smooth-in-a-single-direction

Examples

p <- ggplot(iris) + 
  aes(x = Petal.Width, y = Petal.Length, colour = Species) +
  geom_point()
  
# classic geom_smooth
p + geom_smooth(method = "lm")
#> `geom_smooth()` using formula = 'y ~ x'


# use `fullrange = TRUE` to extend on both sides
p + geom_smooth(method = "lm", fullrange = TRUE)
#> `geom_smooth()` using formula = 'y ~ x'


p + geom_smooth(method = "lm", xseq = c(.75, 2.25))
#> `geom_smooth()` using formula = 'y ~ x'


# use `method = "lm_right"` or `method = "lm_left"`
# with `fullrange = TRUE` to extand in only one direction
p + geom_smooth(method = "lm_right", fullrange = TRUE)
#> `geom_smooth()` using formula = 'y ~ x'

p + geom_smooth(method = "lm_left", fullrange = TRUE)
#> `geom_smooth()` using formula = 'y ~ x'


# use `method = "lm_zero"` to include zero
p + geom_smooth(method = "lm_zero")
#> `geom_smooth()` using formula = 'y ~ x'