X axis labels begin at the middle and do not match data points

Question

I either seem to be running in circles or there is something wrong with my data. I want to plot some data and use ?axis to modify the labels on the X axis.

I have two issues however:

1. The axis labels begin in the center of the x-axis instead of at the beginning
2. The axis labels do not match the data points in the plot

I would like to have X axis labels ranging from 10 to 90 by 5.

This is the code that I use and came up with so far:

values <- cbind(1:180,1)

l <-    list(1:10,11:20,21:30,31:40,41:50,51:60,61:70,71:80,81:90,91:100,101:110,111:120,121:130,131:140,141:150,151:160,161:170,171:180)
# compute mean across the intervals in l
meanqual <- sapply(l, function(x) mean(values[x,1]))
meanqual
plot <- plot(meanqual, type="o", xlab="% Size of Wave", ylab="Values",xaxt='n', lty=1)
legend('bottomright', c("Values"),pch=21, lty=1, cex=1)
axis(side=1, at= seq(10,90,5))

Answer 1

If you only give one numeric vector to plot it "assumes" you meant to use the position or index of the values in that vector as the x values, so the plot call plotted meanqual against 1:length(meanqual) . If you wanted to plot against the seq() argument you latter used in the axis call you should supply it (or rather something similar in scale with the same length as meanqual ) to plot :

plot <- plot(x=seq(5,90,5), y=meanqual, type="o", 
             xlab="% Size of Wave", ylab="Values",xaxt='n', lty=1)
legend('bottomright', c("Values"),pch=21, lty=1, cex=1)
axis(side=1, at= seq(10,90,5), labels=seq(10,90,5))