title: How to plot the name of a line on a legend without using color, linetype or shape
body: <p>In this plot I want to show on the legend the name ("c") of the red solid line. How can I do it since that line must be of 'red' color, be 'solid' and have no 'point shape'?</p>
  
  <p>How can I show in that situation the name of the 'c' line on a legend?</p>
  
  <pre class="lang-r prettyprint-override"><code>library(tidyverse)
  
  df1 &lt;- tibble(line_label = c('a', 'a', 'b', 'b'),
               year = c(2010, 2012, 2010, 2012),
               value = c(0.1, 0.2, 0.3, 0.4))
  df2 &lt;- tibble(line_label = c('c', 'c'),
                year = c(2010, 2012),
                value = c(0.15, 0.35))
  
  p &lt;- ggplot(data = df1, aes(x = year, y = value)) +
    geom_line(aes(color = line_label), size = 1) +
    scale_linetype_manual(values=c("solid", "dashed"),
                          guide = guide_legend(ncol = 2)) +
    geom_point(aes(shape = line_label, color = line_label), size = 2) +
    geom_line(data = df2, aes(x = year, y = value),
              alpha = .8, size = 2, color = "#DA2537") +
    scale_color_manual(values=c("#BFBFBF", "#173C70")) +
    scale_x_continuous(breaks=seq(2010, 2012, by = 1)) 
  plot(p)
  </code></pre>
  
  <p><img src="https://i.imgur.com/sdHKELP.png" alt=""></p>
  
  <p><sup>Created on 2019-10-30 by the <a href="https://reprex.tidyverse.org" rel="nofollow noreferrer">reprex package</a> (v0.3.0)</sup></p>