R: Plot multiple lines on the same axis with the average in bold?

I have some data that looks like this:

df <- data.frame(time=1:6, a=c(100, 90, 91, 92, 91, 91.5), b=c(99.9, 90.3, 90.9, 91.8, 92, 91.5), c=c(100.3, 88.5, 90.5, 91.5, 91, 91.3))
df <- data.frame(df, mean=apply(df[,2:4], 1, mean))
> df
  time     a    b     c      mean
1    1 100.0 99.9 100.3 100.06667
2    2  90.0 90.3  88.5  89.60000
3    3  91.0 90.9  90.5  90.8000开发者_运维问答0
4    4  92.0 91.8  91.5  91.76667
5    5  91.0 92.0  91.0  91.33333
6    6  91.5 91.5  91.3  91.43333

I want to plot the lines on the same canvas with time on the x-axis. I want the lines a, b, and c to be slightly transparent (or lightly colored) and the mean to be bold and very clear.

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Okay, this time in ggplot! First you have to melt your df down to one point per line, then the ggplot magic:

dfm = melt(df,"time",c("a","b","c","mean"))
ggplot(dfm)+geom_line(
  aes(x=time,y=value,colour=variable)) + 
  scale_colour_manual(values=c("#FF000080","#00FF0080","#0000FF80","black"))

---

In base graphics, matplot:

matplot(df$time,df[,c("a","b","c","mean")],
  type="l",
  col=c("#FF000040","#00FF0040","#0000FF40","black"),
  lty=1,lwd=3)

tweak the colours to your taste. Note that arguments are repeated so all lines have lty=1 and lwd=3, but the colours are individual.

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Spacedman doesn't do lattice, but it seems fairly straightforward:

   xyplot(a+b+c+mean ~ time, data=df, type="l", 
           col=c("#FF000080","#00FF0080", "#0000FF80","black"))