[R] how to specify the location of tick mark on x axies

[Duncan Murdoch]

Xin wrote:
> Dear:
>
>     I want to plot barplot and let bar be in the middle of each x axis category.
>  
>    Do you have this experience?
>  
>    Many Thanks!
>
>    Xin
> 	[[alternative HTML version deleted]]
>
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> and provide commented, minimal, self-contained, reproducible code.
>   
 > x <- rnorm(100)
 > h <- hist(x, axes=F)
 > str(h)
List of 7
 $ breaks     : num [1:10] -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
 $ counts     : int [1:9] 2 7 23 17 28 9 10 2 2
 $ intensities: num [1:9] 0.04 0.14 0.46 0.34 0.56 ...
 $ density    : num [1:9] 0.04 0.14 0.46 0.34 0.56 ...
 $ mids       : num [1:9] -1.75 -1.25 -0.75 -0.25 0.25 0.75 1.25 1.75 2.25
 $ xname      : chr "x"
 $ equidist   : logi TRUE
 - attr(*, "class")= chr "histogram"
 > axis(1, at=h$mids)

I'd say that graphically it's not the best idea, but it's not hard to 
do.  If you want variations, see the manual pages ?hist, ?axis, etc.

Duncan Murdoch