Odd behavior of mtext in R

Question

I am trying to design a fairly customized plot in R.

One thing I want to do is add tick marks that are different from the labels - that is, only every 5th tick mark will be labeled. I didn't see an easy way to do this, so I did this:

plot(x = Freq_, y = Mean_ipsi, 
     pch = 20,
     ylim = c(-0.5, .9),
     col = 1 + (ProbF < .05) + (ProbF < .01),
     xaxt = 'n',
     xlab = "Frequency (MHz)", ylab = "z-in minus z-out",
     main = "Temporal, Engle 1, Epi, subjectwise",
     yaxt = 'n')
mtext(text = seq(1.56, 35.1, by = 1.95),
      side = 1, at = seq(1.56, 35.1, by = 1.95), cex = .5,line = 0.25)
axis(1, at = Freq_, tick = TRUE, labels = NA)

and it worked just as I wanted.

But when I changed some of the code preceding mtext I got unexpected results

plot(x = Freq_, y = Mean_ipsi, 
     pch = 20,
     ylim = c(-0.5, .9),
     col = "red",
     xlab = "Frequency (MHz)", ylab = "z-in minus z-out",
     main = "Temporal, Engle 1, Epi, subjectwise 
     \n p values for difference between ipsi and contra",
     yaxt = 'n', type = 'o')
mtext(text = seq(1.56, 35.1, by = 1.95),
      side = 1, at = seq(1.56, 35.1, by = 1.95),
      cex = .5,line = 0.25)
axis(1, at = Freq_, tick = TRUE, labels = NA)

Now, in addition to the x-axis being labeled with every numbers 1.56, 3.51, etc. I get large numbers (cex = 1, I think) at 5, 10 and so on. I don't want these.

I have no idea what is happening here.

Can you provide [a reproducible example?](http://stackoverflow.com/q/5963269/1003565) — Dason, Dec 08 '12 at 00:09
It will be hard, as the data is private, but I will try in a bit — Peter Flom, Dec 08 '12 at 00:17

bill_080 · Accepted Answer · 2012-12-08T01:32:45.970

You're missing xaxt="n" in your second version.

Freq_ <- seq(1.56, 35.1, by = 1.95)
Mean_ipsi <- (0.01 * Freq_)
ProbF <- 0.0

#First Version  
plot(x = Freq_, y = Mean_ipsi, 
     pch = 20,
     ylim = c(-0.5, .9),
     col = 1 + (ProbF < .05) + (ProbF < .01),
     xaxt = 'n',
     xlab = "Frequency (MHz)", ylab = "z-in minus z-out",
     main = "Temporal, Engle 1, Epi, subjectwise",
     yaxt = 'n')
mtext(text = seq(1.56, 35.1, by = 1.95),
      side = 1, at = seq(1.56, 35.1, by = 1.95), cex = .5,line = 0.25)
axis(1, at = Freq_, tick = TRUE, labels = NA)

#=============================================

#Second Version
plot(x = Freq_, y = Mean_ipsi, 
     pch = 20,
     ylim = c(-0.5, .9),
     col = "red",
     xlab = "Frequency (MHz)", ylab = "z-in minus z-out",
     main = "Temporal, Engle 1, Epi, subjectwise 
     \n p values for difference between ipsi and contra",
     yaxt = 'n', type = 'o')  ##### <----- add xaxt="n" here #####
mtext(text = seq(1.56, 35.1, by = 1.95),
      side = 1, at = seq(1.56, 35.1, by = 1.95),
      cex = .5,line = 0.25)
axis(1, at = Freq_, tick = TRUE, labels = NA)

Thanks! I did not see that – Peter Flom Dec 08 '12 at 01:43 — Peter Flom, Dec 08 '12 at 01:43

Odd behavior of mtext in R

1 Answers1