x轴标签与条形不匹配

Question

Hello I am trying to create a stacked barplot using the following code:

test <- as.matrix(read.csv(file="test4.csv",sep=",",head=TRUE))
test <- test[,2:ncol(test)]
pdf(file="test.pdf", height=4, width=6)
par(lwd = 0.3)
barplot(test, space=0.4, xaxt='n', ann=FALSE)
axis(1, cex.axis=0.25, las=2, at=1:ncol(test), space=0.4, labels=colnames(test))
dev.off()

And I get:

As you can see the labels in the x-axis do not match the bars in the plot. Also, the ticks are huge. Can you guys help me beautify the x axis? Thanks so much

Answer 1

Try storing the returned value of the call to barplot() in a named object, and then passing that in to the at= argument of axis() :

xLabLocs <- barplot(test, space=0.4, xaxt='n', ann=FALSE)
axis(1, cex.axis=0.25, las=2, at=xLabLocs, 
     space=0.4, labels=colnames(test))

This may look odd, but it is explained in the Value section of the ?barplot help file:

 Value: A numeric vector (or matrix, when 'beside = TRUE'), say 'mp', giving the coordinates of _all_ the bar midpoints drawn, useful for adding to the graph. 

You just made the (easy enough to make) mistake of assuming that the x-axis coordinates of the bar centers are at 1:n, where n is the number of bars. That's not necessarily true, so it's nice that a single call to barplot() will both: (a) plot the bar plot as its side effect; and (b) return the necessary x-axis coordinates as its return value.