r - How can I label the x-intercept of a vertical abline? - Stack Overflow

I have a plot that shows a curve and a couple of ablines:

The plot is created using the curve command. I would like to add the value of the x-intercept below the x-axis . . . is this possible without using a more sophisticated graphing package?

Thanks!!!

I have a plot that shows a curve and a couple of ablines:

The plot is created using the curve command. I would like to add the value of the x-intercept below the x-axis . . . is this possible without using a more sophisticated graphing package?

Thanks!!!

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Share Improve this question Follow asked Jan 2 at 19:33 GuyMatzGuyMatz 69966 silver badges1010 bronze badges 1

• 3 Could you edit your question to include sufficient code/data so that it can be reproducible? – jpsmith Commented Jan 2 at 19:36

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2 Answers 2

Sorted by: Reset to default 1

In base R you can use mtext to add it in. For the x-axis, side = 1:

x_abline <- -0.25

curve(x ^ 3 - 3 * x, -2, 2)
abline(v = x_abline, col = "red", lty = 2)
mtext(x_abline, side = 1, at = x_abline)

Or axis:

curve(x ^ 3 - 3 * x, -2, 2)
abline(v = x_abline, col = "red", lty = 2)
axis(1, x_abline)

USe axis as shown

plot(1)
abline(v = 1.1)
axis(1, 1.1)