title: Plotting histogram+linespoints in Gnuplot
body: <p>I would like to connect selected bars in a histogram with linespoints. Now</p>
  
  <p>I have created the histogram using the following code in Gnuplot: </p>
  
  <pre><code>set terminal postscript eps enhanced colour font 'Times-Roman,12' size 6in,4in  
  set output "LS_Figure_Histogram_New_2019_III.eps"
  
  set xtics out scale 1.5 
  set ytics out scale 1.5
  set y2tics out scale 1.5 
  set ytics nomirror
  set yrange [-3.50:-3.70]
  set y2range [0:45] 
  set key off
  set tics font ", 14"
  set xlabel "Experiment No." font ",16"
  set ylabel "Li^{+}|Li vs. Cl^{-}|Cl_{2} (V)" font ",16"
  set y2label "Residual Current Density (mA/cm^{2})" font ",16"
  set key autotitle columnheader
  set key inside left horizontal
  set style fill solid 1.00 noborder
  set style histogram clustered gap 1 title textcolor lt -1
  
  
  set style data histograms
  plot 'LS_Histogram_Comp_2019.dat' using 2:xtic(1) ls 2 ti col axis x1y1, '' u 3:xticlabels(1) ls 4 ti col axis x1y2
  </code></pre>
  
  <p>The data file is as given below </p>
  
  <pre><code># Histogram_Comparison of onset potential &amp; Residual current density
  Experimental "Li^{+}|Li (V)" "Res. Current Density (mA/cm^{2})" 
  1   -3.64469    31.3
  2   -3.65257    11.2
  3   -3.66159    32.39
  4   -3.66536    13.41
  5   -3.66314    16.3
  6   -3.64556    10.3
  7   -3.64383    10.08
  8   -3.63042    9.96
  9   -3.65344    9.59
  10  -3.64383    8.44
  11  -3.64859    11.1
  12  -3.63919    27.6
  13  -3.64204    9.78
  14  -3.62692    30.96
  15  -3.64348    18.22
  16  -3.6362         32.05
  17  -3.62831    20.1
  18  -3.62984    42.32
  19  -3.63764    24.8
  </code></pre>
  
  <p>I wish to connect bars corresponding to Experimental 12, 14, 16 and 18 (using col 1 and 3 data) and bars 13, 15, 17 and 19 (using col 1 and 3 data) using linespoints. </p>
  
  <p>Is there a way to do it in Gnuplot?</p>