Label an axis generated by axis() function

Question

I'm plotting a dual axis graph in r base and I can't add a label to the secondary axis. Here's what I'm working with:

dados = structure(list(IDADE = c(65L, 35L, 65L, 42L, 50L, 44L, 0L, 58L, 
                             22L, 27L, 34L, 31L, 0L, 24L, 34L, 20L, 4L, 34L, 20L, 27L, 8L, 
                             2L, 20L, 31L, 45L, 26L, 26L, 40L, 50L, 34L), ESTADO = c(1L, 1L, 
                                                                                     1L, 1L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 
                                                                                     1L, 1L, 1L, 0L, 1L, 1L, 1L, 1L, 0L, 1L, 0L, 0L), TIPINT = c(3L, 
                                                                                                                                                 1L, 3L, 2L, 3L, 2L, 2L, 3L, 1L, 1L, 1L, 1L, 2L, 1L, 2L, 1L, 2L, 
                                                                                                                                                 3L, 2L, 2L, 2L, 3L, 3L, 2L, 2L, 1L, 3L, 2L, 3L, 1L), DIARIAS = c(2L, 
                                                                                                                                                                                                                  2L, 4L, 1L, 1L, 1L, 10L, 1L, 2L, 2L, 2L, 3L, 3L, 1L, 2L, 3L, 
                                                                                                                                                                                                                  6L, 10L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 3L, 6L, 1L, 1L, 2L)), .Names = c("IDADE", 
                                                                                                                                                                                                                                                                                        "ESTADO", "TIPINT", "DIARIAS"), row.names = c(NA, 30L), class = "data.frame")

#Define boxplot base
bx = boxplot(dados$IDADE~dados$TIPINT,axes=F, xlab=NA,ylab=NA,col=heat.colors(3,0.6))

#Posiciona eixos
par(mar = c(5,5,2,5))

#Plota bar
barplot(table(dados$TIPINT),col=heat.colors(3,0.4),names=c("Tipo 1","Tipo 2","Tipo 3"),
    ylab = "Quantidade de pacientes")

#Plota box
par(new=T)
bx2 = bxp(bx,boxwex = 0.50, at = c(0.9, 2,3.1),axes=F, xlab=NA, ylab="l",boxfill=heat.colors(3,0.7))
axis(side=4)

Which gets me the following graph

I'm trying to label the right axis, but axis(side=4,labels="labels") is for something else and axis(side=4,ylab="label") doesn't work.

Thanks

Answer 1

You can use the function mtext to add a label to a secondary axis, using the line=2 argument to move it the appropriate distance from the axis.

mtext("label", 4, line=2)

Alternatively you could use just text to have finer control, if say, you want to reorient the label. You can pull the plot dimensions from par("usr") and adjust accordingly.

p <- par("usr")
text(p[2]+0.4, mean(p[3:4]), labels = "label", xpd=NA, srt = -90)