Adding Straight Lines to a Plot in R Programming – abline() Function
Last Updated :
14 Jul, 2020
abline()
function in R Language is used to add one or more straight lines to a graph. The abline()
function can be used to add vertical, horizontal or regression lines to plot.
Syntax:
abline(a=NULL, b=NULL, h=NULL, v=NULL, …)
Parameters:
a, b: It specifies the intercept and the slope of the line
h: specifies y-value for horizontal line(s)
v: specifies x-value(s) for vertical line(s)
Returns: a straight line in the plot
Example 1: To add a vertical line to the plot
plot (cars)
abline (v = 16, col = "darkgreen" )
plot (cars)
abline (v = c (16, 22), col = c ( "darkgreen" , "blue" ),
lty = c (1, 2), lwd = c (1, 3))
set.seed (1200); mydata<- rnorm (180)
hist (mydata, col= "darkgreen" )
abline (v = mean (mydata), col = "blue" , lwd = 4, lty = 4)
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Output:
Here, in above example straight line is added using abline() to different graphical plots
Example 2: To add a horizontal line
plot (cars)
abline (h = 60, col = "darkgreen" )
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Output:
In above example abline()
Function draws an horizontal line on the current plot at the specified ‘x’ coordinates.
Example 3: To add a regression line
par (mgp = c (2, 1, 0), mar = c (3, 3, 1, 1))
require (stats)
reg<- lm (dist ~ speed, data = cars)
coeff = coefficients (reg)
eq = paste0 ( "y = " , round (coeff[1], 1), "*x " ,
round (coeff[2], 1))
plot (cars, main = eq)
abline (reg, col = "darkgreen" )
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Output:
In the above example, straight-line is added using the line equation and abline()
function and plot relation between speed and distance.
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