title: How to modify legends in ggplot2 (R) when combining bar and line charts?
body: <p>Following is my sample df and the plot from ggplot2. As you can see, bms appear twice in the legend. How do I keep bms with line only in legend and omit the bms with filled in square(fyi:bms=nda+nfa)?</p>
  
  <pre><code>df&lt;-structure(list(date = structure(c(16450, 16481, 16509, 16540, 
  16570, 16601, 16631, 16662, 16693, 16723, 16754, 16784, 16450, 
  16481, 16509, 16540, 16570, 16601, 16631, 16662, 16693, 16723, 
  16754, 16784, 16450, 16481, 16509, 16540, 16570, 16601, 16631, 
  16662, 16693, 16723, 16754, 16784), class = "Date"), growth = c(15.6208780039999, 
  15.1694006447267, 16.195618338681, 16.0691510104003, 19.00531067356, 
  20.6393420328606, 19.913212909657, 20.1086270676403, 20.9905103619554, 
  21.6087938989033, 24.1841921678774, 24.9969801670078, 16.7740140352366, 
  19.0872278878704, 20.6172095631277, 18.3422520752069, 18.0117650156554, 
  17.0745150898952, 16.9399643028229, 16.4777161388574, 13.6874693641892, 
  13.5642463172163, 15.1097777196027, 13.395801323272, 13.8035044502667, 
  9.32224304536525, 9.50933290655784, 12.5344406713178, 20.5191805086465, 
  26.2642712998039, 24.7100853142004, 25.7997724265002, 32.7241081094385, 
  34.9437659017955, 39.1086559617412, 43.4779253836789), contribution_growth = c(15.6208780039999, 
  15.1694006447267, 16.195618338681, 16.0691510104003, 19.00531067356, 
  20.6393420328606, 19.913212909657, 20.1086270676403, 20.9905103619554, 
  21.6087938989033, 24.1841921678774, 24.9969801670078, 10.2624309484927, 
  11.4292066393698, 12.4103419775945, 11.1633356429028, 10.8747304989152, 
  10.4510867812205, 10.457861232512, 10.0596987226562, 8.43653450851318, 
  8.46037929729901, 9.39649462921924, 8.22970711412679, 5.35844705550725, 
  3.7401940053569, 3.78527636108649, 4.90581536749757, 8.13058017457733, 
  10.1882552516401, 9.45535167720894, 10.0489283449197, 12.5539758534422, 
  13.1484146016662, 14.7876975386582, 16.7672730529425), components = c("bms", 
  "bms", "bms", "bms", "bms", "bms", "bms", "bms", "bms", "bms", 
  "bms", "bms", "nda", "nda", "nda", "nda", "nda", "nda", "nda", 
  "nda", "nda", "nda", "nda", "nda", "nfa", "nfa", "nfa", "nfa", 
  "nfa", "nfa", "nfa", "nfa", "nfa", "nfa", "nfa", "nfa")), .Names = c("date", 
  "growth", "contribution_growth", "components"), row.names = c(NA, 
  -36L), class = "data.frame")
  
  df&lt;-    date    growth contribution_growth components
  1  2015-01-15 15.620878           15.620878        bms
  2  2015-02-15 15.169401           15.169401        bms
  3  2015-03-15 16.195618           16.195618        bms
  4  2015-04-15 16.069151           16.069151        bms
  5  2015-05-15 19.005311           19.005311        bms
  6  2015-06-15 20.639342           20.639342        bms
  7  2015-07-15 19.913213           19.913213        bms
  8  2015-08-15 20.108627           20.108627        bms
  9  2015-09-15 20.990510           20.990510        bms
  10 2015-10-15 21.608794           21.608794        bms
  11 2015-11-15 24.184192           24.184192        bms
  12 2015-12-15 24.996980           24.996980        bms
  13 2015-01-15 16.774014           10.262431        nda
  14 2015-02-15 19.087228           11.429207        nda
  15 2015-03-15 20.617210           12.410342        nda
  16 2015-04-15 18.342252           11.163336        nda
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/KkAfH.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KkAfH.jpg" alt="enter image description here"></a></p>
  
  <p>Code: </p>
  
  <pre><code>library(ggplot2)
  test_plot&lt;-ggplot(
    df[df$components!="bms",],
    aes(x=date,y=contribution_growth,fill=components))+
    geom_bar(stat='identity')+
    geom_line(data=df[df$components=="bms",],
              aes(x=date,y=growth,color=components))+
    scale_x_date(date_breaks = "2 month", date_labels = "%Y %b")+
    labs(
      title = "Contributions to m2 growth"
      ) +
  
    theme_bw()+  # black and white theme
    theme(
      plot.title = element_text(hjust = 0.0, size=10, face="bold", color="blue"),
      plot.subtitle = element_text(hjust = 0.0, size=8, color="blue"),
      plot.caption = element_text(hjust = 0.0, size=8),
      axis.title.x=element_blank(),
      axis.text.x=element_text(size=8, angle=90),
      axis.text.y=element_text(size=8),
      axis.title.y=element_blank(),
      legend.title=element_blank(),
      legend.key = element_blank(),
      legend.text=element_text(size=8),
      legend.direction="horizontal",
      legend.position="top",
      legend.background = element_rect(fill = FALSE),
      panel.grid.major =  element_line(colour = NA, size = 0.0),
      panel.grid.minor =  element_line(colour = NA, size = 0.0),
      panel.border = element_blank(),
      axis.line = element_line(color = 'black')
    )
  </code></pre>