# grconvertX and grconvertY

**R – Insights of a PhD**, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

These two functions are unbelievably useful for positioning graphical elements (text, axes, labels, …) in R. They allow one to convert coordinates between various different formats. For instance, you can convert your user coordinate (say 5 where x ranges from 0 to 200) to normalized device coordinates (proportional distance across the device) and vice versa. Very useful for positioning panel labels…

grconvertX(.1, "npc", "user")

returns the x coordinate that is 10% across the plot region. So with that and the equivalent y function, you can place your labels in exactly the same position on every panel and plot… e.g.

plot(rnorm(20), rnorm(20)) text(grconvertX(.1, "npc", "user"), grconvertY(.9, "npc", "user"), "a)")

To show the difference between the from side, run the following…

text(grconvertX(.1, "npc", "user"), grconvertY(.9, "npc", "user"), "npc") text(grconvertX(.1, "ndc", "user"), grconvertY(.9, "ndc", "user"), "ndc", xpd = "n") # the text will be near the outer margin

It’s also very useful for positioning axis labels from boxplot when the labels are too long…

Hope that’s helpful to someone…

**leave a comment**for the author, please follow the link and comment on their blog:

**R – Insights of a PhD**.

R-bloggers.com offers

**daily e-mail updates**about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.