Adjusting x-axis label names in barchart in R base plotting

Question

How do I adjust the position of the x-axis labels in this bar plot? I would ideally make each name left justified of centered?

Here is my code:

data <- read.csv('CNV_bar_DF.csv')

f<-"CNV_data.png"
png(f,width=1000, height=1000)

par(fig=c(0.0,1.0,0.5,1.0)) #   FINE POSITIONING, x1,x2,y1,y2
barplot(data$Amplification, names=data$Gene, cex.names=1.0, las=2, ylim=c(0,60), col=colors()[c(0,81,0)]) 

par(fig=c(0.0,1.0,0.05,0.55), new=TRUE) #   FINE POSITIONING, x1,x2,y1,y2
barplot(data$Deletion, ylim=rev(c(0,60)), col=colors()[c(0,137,0)])

dev.off()

The column labelled 'Gene' is what I mean by x-axis label. Currently it is right justified but I would like it in the center. If there is a better way to write the label then suggestions are very welcome.

here is the dataframe:

    Gene    Deletion    Amplification   Total
KIAA0100    2   43  45
DNAH9   44  0   44
BPTF    0   38  38
PDCD11  32  1   33
PREX2   3   30  33
RAD51C  0   31  31
CSMD3   0   30  30
ENPP2   0   29  29
STAT3   0   28  28
CPXM2   24  1   25
SOCS7   0   25  25
STAT5B  0   24  24
ACADSB  22  1   23
CSMD1   8   14  22
FAM208B 1   21  22
GOLGA7B 22  0   22
STAT5A  0   22  22
AXIN2   0   21  21
UNC45B  0   21  21
GAD2    20  0   20
SLC6A4  0   20  20
ANK3    19  0   19
APBB1IP 19  0   19
C17orf47    0   19  19
PRKCQ   0   19  19
TSPYL5  0   19  19
CRHR1   1   17  18
CDH23   16  0   16
TET1    15  0   15
CDHR1   14  0   14
FAM110B 0   14  14
FAM83A  0   12  12
GPR158  10  2   12
KIAA1244    12  0   12
ELAVL2  11  0   11
LRRC6   1   10  11
PTPRK   9   2   11
SASH1   10  1   11
BRCA2   10  0   10
ENPEP   6   4   10
FAM171A2    0   10  10
RFX6    9   1   10

here is an image of the output:

Answer 1

Try this (comments inline):

png(f, 1000, 1000)

par(fig=c(0.0,1.0,0.5,1.0)) 
pos <-   # the result of barplot is the location of the midpoints for axis construction
   barplot(data$Amplification, xaxt="n", # suppresses x-axis printing
                ylim=c(0,60), col=colors()[c(0,81,0)]) 
axis(1,           # now make the x-axis
     las=2, hadj=0.5, # this "centers" the text
     at=pos,          # this uses the return result of `barplot`
     lab=data$Gene, 
     line=2,   # the 'line' argument needed to adjust the vertical "centerline"
     col="transparent")   # needed to suppress drawing an "axis-line"
par(fig=c(0.0,1.0,0.05,0.55), new=TRUE) 
barplot(data$Deletion, ylim=rev(c(0,60)), col=colors()[c(0,137,0)])

dev.off()

Tested with png(f, 1000,1000) and seems to deliver acceptable results to my eye. This is somewhat like a pyramid-plot although those are arranged vertically. They are typically used to display compare proportions of populations by age-groups of men and women in demographic literature. I know there is an implementation of pyramid plots in the plotrix package. If you are using base-graphics, checking out the added capacities in pkg:plotrix would be a good idea.