在条形图中设置轴标签和刻度线的不同位置

我想重新对齐/偏移条形图的 x 轴和相关刻度线。这应该很简单，但我很难找到答案。下面是一些包含 24 个类别的示例数据。

xval = c(1:24)
count = c(0.03,0.03,0.08,0.06,0.11,0.4,0.3,0.5,0.5,0.6,0.4,0.1,0.1,0.4,0.2,0.1,0.06,0.05,0.03,0.02,0.01,0.03,0.01,0.02)
df = as.data.frame(cbind(xval, count))

我可以使用以下代码轻松生成一个条形图，其刻度线在条形中点对齐：

mp <- barplot(df$count, space=0, axes=FALSE) 
axis(side=2, pos=-0.2)
axis(side=1, at =mp, labels=df$xval)

我还可以使用以下命令移动整个 x 轴（标签和刻度）以与条形外部对齐（尽管现在无法将最后一个条形合并到轴中）：

axis(side=1, at =mp-0.5, labels=df$xval)

虽然我希望 x 轴和关联的刻度线与条形边界对齐（即刻度线位于条形图的两侧而不是中心），但我希望 x 轴标签保留在条形图的中点。有没有一种简单的方法可以实现这一目标？

这是你想要的？

# create positions for tick marks, one more than number of bars
at_tick <- seq_len(length(count) + 1)

# plot without axes
barplot(count, space = 0, axes = FALSE) 

# add y-axis
axis(side = 2, pos = -0.2)

# add x-axis with offset positions, with ticks, but without labels.
axis(side = 1, at = at_tick - 1, labels = FALSE)

# add x-axis with centered position, with labels, but without ticks.
axis(side = 1, at = seq_along(count) - 0.5, tick = FALSE, labels = xval)