[R] How to plot with txt or symbol instead of number as x-axis scale ?

[Yong Wang]

Dear R-list

My question is exactly as the subject, I did search the archieve but
failed to find relevant message, in more details:

The simplest example, 4 factors and 4 value like below:
10    20      30     40
A       B        C      D

if I plot the value, the x-axis will be scaled as 1,2,3,4 with each
represent a level. How can I change the x-axis scale to A,B,C,D ?

Regards
young