# [R] I want axes that cross

Mark Difford mark_difford at yahoo.co.uk
Mon Feb 16 10:14:40 CET 2009

```Hi Paul,

>> Have you ever seen a drawing of the regions of an R plot with the
>> terminology that is used for parts?

>From what I can remember, several documents on CRAN cover this. The one that
springs to mind is Alzola & Harrell's "An Introduction to S and the Hmisc

Chap. 4 of MASS by Venables & Ripley (4th ed.) will also give you what you
want.

Regards, Mark.

Paul Johnson-11 wrote:
>
> On Fri, Feb 13, 2009 at 3:14 PM, Marc Schwartz
> <marc_schwartz at comcast.net> wrote:
>> on 02/13/2009 02:19 PM Paul Johnson wrote:
>>> On Fri, Feb 13, 2009 at 1:51 PM, Marc Schwartz
>>
>> OK, so given all of the above, something like the following should work:
>>
>> set.seed(1233240)
>> x <- rnorm(100)
>> z <- gl(2,50)
>> y <- rnorm(100, mean = 1.8 * as.numeric(z))
>>
>> # Calculate a new range, subtracting a definable value
>> # from the min of each vector for the new minimum
>> # Adust the 0.25 as may be needed
>> X <- c(min(x) - 0.25, max(x))
>> Y <- c(min(y) - 0.25, max(y))
>>
>> # Use 'X' and "Y' here, not 'x' and 'y'
>> # So that the plot region is extended appropriately
>> plot(X, Y, type = "n", axes = F, xlab = "x", ylab = "y")
>>
>> points(x, y, pch = "\$", cex = 0.7, col = z)
>>
>> # DO use 'pos'...
>> axis(1, pos = Y[1], col = "green", col.axis = "green")
>> axis(2, pos = X[1], col = "red", col.axis = "red")
>>
>> # get the plot region boundaries
>> usr <- par("usr")
>>
>> segments(X[1], usr[3], X[1], usr[4], col = "red")
>> segments(usr[1], Y[1], usr[2], Y[1], col = "green")
>>
>>
>> HTH,
>>
>> Marc
>>
>>
>
> Thanks, Marc and everybody.
>
> This last suggestion produces the graph I was trying for.
>
> The other approaches that people suggest, using pos or xaxp, produce
> other undesired changes in the tick marks or the position of the axes
> relative to the data. xaxp offers the promise of a more intuitive
> solution, except that, when using it, the tick marks are pushed off in
> a bad way.  Your use of segments to draw the extensions of the axes
> was the first intuition I had, but I did not know about the trick you
> used to retrieve the size of the usr box.
>
> More secrets of par, revealed.
>
> Have you ever seen a drawing of the regions of an R plot with the
> terminology that is used for parts?  Until I saw your example code, I
> had not understood that the plot axes are placed at the absolute edge
> of the user plotting region, for example.
>
> --
> Paul E. Johnson
> Professor, Political Science
> 1541 Lilac Lane, Room 504
> University of Kansas
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>

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