图例没有出现在具有两个不同 geom_line() 的 ggplot 中

Question

I have my data shown as below:

library(ggplot2)
library(RColorBrewer)      

Year_2012_2017 <- data.frame(a=c(5,4,2,5,4,6,6,12,7,7,6,3),
                  b=c(6,4,1,2,9,7,4,7,8,12,2,4),
                  c=c(1,1,6,4,5,7,11,14,10,6,7,8),
                  d=c(4,9,5,3,4,11,9,11,10,8,4,9),
                  e=c(4,4,5,3,1,19,10,11,19,8,7,9),
                  f=c(4,5,3,6,5,12,25,15,21,24,14,1))
Year_2012_2017$mean <- rowMeans(Year_2012_2017)
Year_2012_2017<- transform(Year_2012_2017, Min = pmin(a,b,c,d,e,f), Max = pmax(a,b,c,d,e,f), seq = seq_len(dim(Year_2012_2017)[1]))

Year_2018 <- data.frame(g=c(10,5,7,6,9,26,NA,NA,NA,NA,NA,NA))
Year_2018 <- data.frame(Year_2018,seq1 = seq_len(dim(Year_2018)[1]))

Month_name <- c("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December")

And my graph code:

ggplot(Year_2012_2017) + 
geom_line(aes(factor(seq), mean), group = 1,size=1, color = brewer.pal(7, "Set1")[2],lty=2)+ 
    #Mean of 2012 to 2017

geom_ribbon(aes(x = seq, ymax = Max, ymin = Min, fill= "Min-Max(2012-2017)"),alpha = 0.5)+ 
scale_fill_manual("",values="skyblue")+                                                                   
    #Min and max

geom_line(aes(Year_2018$seq1,Year_2018$g),group = 1,size=1, color = brewer.pal(7, "Set1")[2],lty=1)+ 
    #Year of 2018

coord_fixed(ratio=1/6)+
xlab("Month") +
ylab("Number of case")+
scale_x_discrete(labels=Month_name)+
scale_y_continuous(limits = c(0, 30),breaks=seq(0,30,5))

Which produces the following graph:

two lines and one ribbon

I tried for quite a while but failed to add legend of two geom_line() , can anyone help me find the solution? Thanks in advance :)

Answer 1

Posting this for reference, but it is a direct application of this answer . If you can't rearrange your data so that it's all in one dataframe with common columns, a workaround is to put labels in aes() and you will get a legend:

ggplot(Year_2012_2017) + 
    geom_line(aes(factor(seq), mean, colour = "2012-2017"), group = 1,size=1, lty=2)+ 
    #Mean of 2012 to 2017
    geom_ribbon(aes(x = seq, ymax = Max, ymin = Min, fill= "Min-Max(2012-2017)"),alpha = 0.5)+ 
    scale_fill_manual("",values="skyblue")+                                                                   
    #Min and max
    geom_line(aes(Year_2018$seq1,Year_2018$g, colour = "2018"),group = 1,size=1, lty=1)+ 
    #Year of 2018
    coord_fixed(ratio=1/6)+
    xlab("Month") +
    ylab("Number of case")+
    scale_x_discrete(labels=Month_name)+
    scale_y_continuous(limits = c(0, 30),breaks=seq(0,30,5))