CODEWITHSUNDEEP
rggplot2
SiH
SiH

Reputation: 1546

draw vertical lines in ggplot with faceting

I have line plots y vs x. y is sigmoid and varies from 0 to 1.

  1. determine the value of x where y = 0.5 or very close by interpolation.
  2. draw vertical line at x where y = 0.5
library(tidyverse)

# continuous variables
x <- seq(-5, 5, 0.1)

# compute y1
error_term <- runif(1, min = -2, max = 2)
y1 <- 1/(1 + exp(-x + error_term))

# compute y2
error_term <- runif(1, min = -2, max = 2)
y2 <- 1/(1 + exp(-x + error_term))

# merge y
y <- c(y1, y2)
x <- c(x, x)
# categorical variable
a <- c(rep(0, 101), rep(1, 101))

tbl <- tibble(x, a, y)

# TASK
# 1. determine values of x at which y = 0.5 for all categories and store them in variable x0
# 2. Use x0 to draw vertical lines in plots at x where y is 0.5

# ggplot
ggplot(data = tbl,
       aes(x = x,
           y = y)) + 
  geom_line() + 
  theme_bw() +
  facet_grid(a ~ .)

Upvotes: 0

Views: 213

Answers (1)

MrFlick
MrFlick

Reputation: 206242

This really isn't something built in to ggplot so you'll need to summarize the data yourself prior to plotting. You can write a helper function and then create the data you need for the lines

find_intersect <- function(x,y, target=0.5) {
  optimize(function(z) (approxfun(x,y)(z)-target)^2, x)$minimum
}
line_data <- tbl %>% 
  group_by(a) %>% 
  summarize(xint=find_intersect(x,y))

Then plot with

ggplot(data = tbl,
       aes(x = x,
           y = y)) + 
  geom_line() + 
  theme_bw() +
  geom_vline(aes(xintercept=xint), data=line_data) + 
  facet_grid(a ~ .)

enter image description here

Upvotes: 1

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