updateusr: Updates the 'usr' coordinates in the current plot.
In TeachingDemos: Demonstrations for Teaching and Learning

Description Usage Arguments Details Value Note Author(s) See Also Examples

For a traditional graphics plot this function will update the 'usr' coordinates by transforming a pair of points from the current usr coordinates to those specified.

1	updateusr(x1, y1 = NULL, x2, y2 = NULL)

`x1`	The x-coords of 2 points in the current 'usr' coordianates, or anything that can be passed to `xy.coords`.
`y1`	The y-coords of 2 points in the current 'usr' coordinates, or an object representing the points in the new 'usr' coordinates.
`x2`	The x-coords for the 2 points in the new coordinates.
`y2`	The y-coords for the 2 points in the new coordinates.

Sometimes graphs (in the traditional graphing scheme) end up with usr coordinates different from expected for adding to the plot (for example barplot does not center the bars at integers). This function will take 2 points in the current 'usr' coordinates and the desired 'usr' coordinates of the 2 points and transform the user coordinates to make this happen. The updating only shifts and scales the coordinates, it does not do any rotation or warping transforms.

If x1 and y1 are lists or matricies and x2 and y2 are not specified, then x1 is taken to be the coordinates in the current system and y1 is the coordinates in the new system.

Currently you need to give the function exactly 2 points in each system. The 2 points cannot have the same x values or y values in either system.

An invisible list with the previous 'usr' coordinates from par.

Currently you need to give coordinates for exactly 2 points without missing values. Future versions of the function will allow missing values or multiple points.

Greg Snow, 538280@gmail.com

par

tmp <- barplot(1:4)
updateusr(tmp[1:2], 0:1, 1:2, 0:1)
lines(1:4, c(1,3,2,2), lwd=3, type='b',col='red')

# update the y-axis to put a reference distribution line in the bottom
# quarter

tmp <- rnorm(100)
hist(tmp)
tmp2 <- par('usr')
xx <- seq(min(tmp), max(tmp), length.out=250)
yy <- dnorm(xx, mean(tmp), sd(tmp))
updateusr( tmp2[1:2], tmp2[3:4], tmp2[1:2], c(0, max(yy)*4) )
lines(xx,yy)