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

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

Output:

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Here, in above example straight line is added using abline() to different graphical plots

Example 2: To add a horizontal line

Output:

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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

Output:

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In the above example, straight-line is added using the line equation and abline() function and plot relation between speed and distance.