title: Adding min and max values as whiskers in ggplot
body: <p>Sample data</p>
  
  <pre><code>dat &lt;- structure(list(year = c(1980, 1981, 1982, 1983, 
                      1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 
                      1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 
                      2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014), 
             mean.yield = c(1477.75648556686, 2082.78798946671, 1715.95287060116, 1694.91457026677, 1907.27741251624, 
                      2299.77944711368, 1944.45457204444, 2332.23014830564, 1937.5072312786, 
                      2301.36084850042, 2343.06974401949, 1897.71782987815, 3080.46183605819, 
                      2825.77292866651, 2487.36584426788, 2534.75722997417, 3093.83332655611, 
                      3163.41853753923, 2278.14084963203, 2639.86079242947, 2656.31404329224, 
                      2351.89226744162, 2589.84639268955, 2692.39721213932, 2529.81158941515, 
                      2902.34615481654, 2828.98931197959, 2762.30104195501, 2635.86326170991, 
                      2568.74725294557, 2651.43758815608, 2703.25614409881, 2747.15308120843, 
                      2821.89878248129, 2933.11693226163), 
             max.yld = c(1537.60708649028, 
                         2171.29863798359, 1768.74854486813, 1789.36916707753, 1995.84210430024, 
                         2354.06020071575, 2053.66394129283, 2412.0155018336, 1996.17829678252, 
                         2396.51091307127, 2488.44909281084, 2032.74648952097, 3303.1998152912, 
                         3053.26052365736, 2881.48366025859, 2637.90697074537, 3218.34312636772, 
                         3280.09506675389, 2395.33412516854, 2840.67386500989, 2754.43088176743, 
                         2604.96931198623, 2705.19033898282, 2796.10064804424, 2676.49124801024, 
                         3070.48768976047, 3022.74601947175, 2856.77855666909, 2711.48801275607, 
                         2614.20472283154, 2943.02001137724, 2922.93632378769, 2866.80927224562, 
                         2875.28226346912, 3171.51986043323), 
             min.yld = c(1411.46865062697, 
                         1987.25224650323, 1635.03389892575, 1551.90596491633, 1787.98499366881, 
                         2207.44878742555, 1845.66299576147, 2243.54678049618, 1873.44546707733, 
                         2219.53361649614, 2107.52355423417, 1710.47189603077, 2819.77978390805, 
                         2552.28608023919, 2088.3687315005, 2330.72467231082, 2992.51321436047, 
                         3033.95006763494, 2124.61291993433, 2456.804932555, 2439.9048945899, 
                         2043.10726300988, 2347.74223494172, 2467.56879062196, 2276.01009074814, 
                         2789.30766856972, 2750.67648303084, 2613.06512489394, 2472.29245440674, 
                         2500.27445852508, 2504.67728857491, 2531.46080829744, 2600.35290182939, 
                         2704.84177339319, 2587.00260848201)), row.names = c(NA, -35L), class = c("grouped_df", 
                                                                                                  "tbl_df", "tbl", "data.frame"), vars = "mun.id", drop = TRUE, indices = list(
                                                                                                    0:34), group_sizes = 35L, biggest_group_size = 35L, labels = structure(list(
                                                                                                      mun.id = 1100031L), row.names = c(NA, -1L), class = "data.frame", vars = "mun.id", drop = TRUE))
  </code></pre>
  
  <p>The data has four columns: year, mean yield, max yield and min yield. I plotted the mean yield as follows: </p>
  
  <pre><code> ggplot(dat, aes(x = year, y = mean.yield)) + geom_line() + geom_point() + theme_bw() 
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/WOc2j.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WOc2j.jpg" alt="enter image description here"></a></p>
  
  <p>For each point, how do I add the max yield and the min yield as whiskers. </p>