将表达式（plotmath）放入图例标签的标签

Question

如何将表达式（plotmath）放入以下图例的图例标签中？

我知道How to use Greek symbols in ggplot2?及其中的链接，但每当我使用scale_..._manual函数时，我会获得第二个图例（请参见下文）。

require(ggplot2) 
require(reshape2) 
require(plyr) 

## parameters 
d <- c(2, 5, 10, 20, 50, 100) 
tau <- c("t1", "t2", "t3") 
fam <- c("f1", "f2", "f3", "f4", "f5") 
meth <- c("m1", "m2", "m3", "m4") 

## lengths 
nd <- length(d) 
ntau <- length(tau) 
nfam <- length(fam) 
nmeth <- length(meth) 

## build result array containing the measurements 
arr <- array(rep(NA, nd*ntau*nfam*nmeth), dim=c(nd, ntau, nfam, nmeth), 
      dimnames=list(d=d, tau=tau, fam=fam, meth=meth)) 
for(i in 1:nd){ 
    for(j in 1:ntau){ 
     for(k in 1:nfam){ 
      for(l in 1:nmeth){ 
       arr[i,j,k,l] <- i+j+k+l+runif(1) 
      } 
     } 
    } 
} 

## create molten data 
mdf <- reshape2:::melt.array(arr, formula = . ~ d + tau + fam + meth) # create molten data frame 
mdf$tau. <- factor(mdf$tau, levels=tau, labels=paste("tau==", tau, sep="")) # expression for tau 
mdf$fam. <- factor(mdf$fam, levels=fam, labels=paste("alpha==", fam, sep="")) # expression for family 
meth.labs <- lapply(1:nmeth, function(i) bquote(gamma==.(i))) # expression for methods 

## plot 
ggplot(mdf, aes(x=d, y=value, shape=meth, linetype=meth)) + geom_line() + 
    geom_point() + facet_grid(fam. ~ tau., scales="free_y", labeller=label_parsed) + 
    ## scale_linetype_manual(values=1:4, breaks=meth, labels=meth.labs) + # problem: adds another legend 
    scale_x_continuous(trans="log10", breaks=d, labels=d) + 
    scale_y_continuous(trans="log10") 

Answer 1

如果我使用都scale_*_manual功能我得到一个传说与表达：

ggplot(mdf, aes(x=d, y=value, shape=meth, linetype=meth)) + geom_line() + 
    geom_point() + facet_grid(fam. ~ tau., scales="free_y", labeller=label_parsed) + 
    ## scale_linetype_manual(values=1:4, breaks=meth, labels=meth.labs) + # problem: adds another legend 
    scale_x_continuous(trans="log10", breaks=d, labels=d) + 
    scale_y_continuous(trans="log10") + 
    scale_linetype_manual(breaks = c('m1','m2','m3','m4'),values = 1:4,labels = meth.labs) + 
    scale_shape_manual(breaks = c('m1','m2','m3','m4'),values = 1:4,labels = meth.labs)