Add line to double bar graph in ggplot2

Question

I have the following plot and code. I wish to plot the "Plan" data

Here's a simple version of the data I'm using:

  times=c("12AM", "1AM", "2AM")
  times = factor(times, levels=c("12AM", "1AM", "2AM"),ordered = TRUE)

  graph_df=data.frame(times,
                      c(12,15,18),
                      c(12,16,14),
                      c(12,17,20))
  colnames(graph_df)=c("Time","LY", "TY", "Plan")

Here's the code I'm using for my ggplot:

      library(ggplot2)
      library(scales) 

      df_long=melt(graph_df)

      ggplot(df_long,aes(Time,value,fill=variable))+
            geom_bar(stat="identity",position="dodge")+ 
            theme(text = element_text(size=10),axis.title.y=element_blank(),legend.title=element_blank(),
                  axis.title.x=element_blank(),plot.title = element_text(size=20),
                  axis.text.x = element_text(angle=45, vjust=1,colour = "black"),
                  axis.text.y = element_text(colour = "black"))+
            #scale_y_continuous(expand = c(0,0), limits = c(0,1.1*max(graph_df[,2:4])),labels = dollar)+
            ggtitle("Total Revenue to Plan")

You can run the provided code and see the graph it makes.

Here's my question: How do I make the Plan variable a line over the double bar graph I already have? I added the following to my ggplot

geom_line(aes(x=as.numeric(Time),y=graph_df$Plan))+

but got the error:

Error: Aesthetics must either be length one, or the same length as the dataProblems:graph_df$Plan

Any help would be greatly appreciated!

Answer 1

If you call your original graph g , then use:

  g + geom_line(data = graph_df,
      mapping = aes(x = Time, y = Plan, group = 1),
      inherit.aes = F)

Ggplot works best with data in data frames, so since you already have graph_df keep it there! Also, you have a factor x axis established, so trying to convert your Time to numeric is contradictory.

Typically, when adding a line for multiple categorical values, you need a grouping aesthetic so it knows which points to connect. Since you are only drawing one line, we can just set group to a constant.

Finally, since fill = variable is in your initial plot, that aesthetic will be inherited by your line layer - which is a problem. I solve this by setting inherit.aes = F for the line layer, but as Frank suggests you could also move the fill mapping into the bar layer instead of the initialization... though y = value might still throw things off (I didn't test).