Adding Straight Lines to a Plot in R Programming - abline() Function

# add line to square plot 
# first example : Add one line
plot(cars)
abline(v = 16, col = "darkgreen")

# second example : add 2 lines 
# addline to square plot 
# change line colors, sizes and types
plot(cars)
abline(v = c(16, 22), col = c("darkgreen", "blue"),
                      lty = c(1, 2), lwd = c(1, 3))

# third example
set.seed(1200); mydata<-rnorm(180)
hist(mydata, col="darkgreen")

# lwd=line width, lty =linetype 
abline(v = mean(mydata), col = "blue", lwd = 4, lty = 4) 

# R program to add a horizontal line
# to a plot

# Creating a plot
plot(cars)

# Calling abline() function
abline(h = 60, col = "darkgreen")

par(mgp = c(2, 1, 0), mar = c(3, 3, 1, 1))

# Fit regression line
require(stats)
reg<-lm(dist ~ speed, data = cars)
coeff = coefficients(reg)

# equation of the line : 
eq = paste0("y = ", round(coeff[1], 1), "*x ", 
                    round(coeff[2], 1))

# plot
plot(cars, main = eq)
abline(reg, col = "darkgreen")