使用条形图分组x轴(group x axis using barplot)

 这是我的数据（data.txt）： 
 
    S1    S2   S3    S4   S5   S6    S7   S8    S9   S10  S11
T1  1.6   17   2.2   1    4.4  23.8  0.2  2.8   3.2  0.4  18.2
T2  0     3.5  1.5   0.5  4    3     6.5  21.6  0.5  1    18.6
T3  0     0    0     4.2  4.2  41.7  4.2  0     8.3  4.2  4.2
T4  4     0    0     0    0    12    4    4     4    16   20
T5  31.3  6.3  12.5  0    0    12.5  0    0     6.3  0    0
T6  12.5  0    0     18.8 0    12.5  0    0     6.3  6.3  0
 
 这是我的代码： 
 
data =  read.table("C:/Users/Irwan/Desktop/graph_plot/data.txt", header = TRUE, sep = "\t", row.names = 1)

attach(data)

column = colnames(data)
rows = rownames(data)

x = barplot(as.matrix(data), xaxt = "n", beside = TRUE, legend = rows, ylim = c(0, 50), density = c(30,30,30,30,70,100), angle = c(0,45,90,135,0,0))

label = as.vector(column)

text(x = x + 1.20, y = -1.25, xpd = TRUE, cex = 0.6, srt = 90, label, pos = 2)
 
 不幸的是，我无法正确分组x轴标签。 
 
 我尝试了很多解决方案，这是我到目前为止所得到的。 任何人都可以指导我如何将结果分组到每6个柱上（例如：前6个柱的S1）。 请注意我在R中不是很好，我只能使用预装的R包，因为不知道原因我无法安装任何新包。 谢谢。 
 
 更新 
 
 我稍微改变了一下我的代码，以便它可以很容易地重现。 我的新代码： 
 
y = matrix (1:15, ncol = 5)

x = barplot(as.matrix(y), xaxt = "n", beside = TRUE, legend = c("T1","T2","T3"), ylim = c(0,30), density = c(30,30,30), angle = c(0,45,90))

label = rep(c("S1","S2","S3","S4","S5"), each = 3)

text(x = x + 0.4, y = -1.25, xpd = TRUE, cex = 0.6, srt = 90, label, pos = 2)

This is my data (data.txt):
 
    S1    S2   S3    S4   S5   S6    S7   S8    S9   S10  S11
T1  1.6   17   2.2   1    4.4  23.8  0.2  2.8   3.2  0.4  18.2
T2  0     3.5  1.5   0.5  4    3     6.5  21.6  0.5  1    18.6
T3  0     0    0     4.2  4.2  41.7  4.2  0     8.3  4.2  4.2
T4  4     0    0     0    0    12    4    4     4    16   20
T5  31.3  6.3  12.5  0    0    12.5  0    0     6.3  0    0
T6  12.5  0    0     18.8 0    12.5  0    0     6.3  6.3  0
 
And this is my code: 
 
data =  read.table("C:/Users/Irwan/Desktop/graph_plot/data.txt", header = TRUE, sep = "\t", row.names = 1)

attach(data)

column = colnames(data)
rows = rownames(data)

x = barplot(as.matrix(data), xaxt = "n", beside = TRUE, legend = rows, ylim = c(0, 50), density = c(30,30,30,30,70,100), angle = c(0,45,90,135,0,0))

label = as.vector(column)

text(x = x + 1.20, y = -1.25, xpd = TRUE, cex = 0.6, srt = 90, label, pos = 2)
 
Unfortunately, I'm not able to group x-axis labels correctly.
 
I've try numbers of solution and this is what I get so far. Can anyone guide me on how to group the result on every 6 bars (example: S1 for the first 6 bars). Please bear in my that I'm not very good in R and I only able to use pre-installed R package as I cannot install any new package due to unknown reason. Thank you.
 
UPDATED
 
I have change little bit my code so that it might be easy to reproduce. My new code: 
 
y = matrix (1:15, ncol = 5)

x = barplot(as.matrix(y), xaxt = "n", beside = TRUE, legend = c("T1","T2","T3"), ylim = c(0,30), density = c(30,30,30), angle = c(0,45,90))

label = rep(c("S1","S2","S3","S4","S5"), each = 3)

text(x = x + 0.4, y = -1.25, xpd = TRUE, cex = 0.6, srt = 90, label, pos = 2)

原文：https://stackoverflow.com/questions/29120229