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 |

`x1` |
The x-coords of 2 points in the current 'usr' coordianates,
or anything that can be passed to |

`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

1 2 3 4 5 6 7 8 9 10 11 12 13 14 | ```
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)
``` |

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