In case you have some data not sorted by column (the easiet way to deal with gnuplot), and you want to plot it


Gnuplot definition: (file myplotrow.gpl) 
set terminal x11 1 noraise
set autoscale
set grid
set xdata time
set timefmt "%Y-%m-%d_%H:%M:%S"
set format x "%m/%d\n%H:%M"
plot "data.dat" \
        using 1:(stringcolumn(2) eq "valAAA"? $3:1/0) title "A" lc rgb "blue",\
     "" using 1:(stringcolumn(2) eq "valBBB"? $3:1/0) title "B" lc rgb "red",\
     "" using 1:(stringcolumn(2) eq "valCCC"? $3:1/0) title "C" lc rgb "green",\
     "" using 1:(stringcolumn(2) eq "valDDD"? $3:1/0) title "D" lc rgb "orange",\
     "" using 1:(stringcolumn(2) eq "valEEE"? $3:1/0) title "E" lc rgb "purple",\
     "" using 1:(stringcolumn(2) eq "valFFF"? $3:1/0) title "F" lc rgb "violet"

pause 100
reread

That you can launch with : 
gnuplot < myplotrow.gpl

Or, if you change the output in the first line :
set terminal postscript color


with :
gnuplot < myplotrow.gpl > myoutput.ps


Exemple values :
2015-09-24_10:00:00 valAAA 37.000
2015-09-24_10:00:00 valBBB 37.000
2015-09-24_10:00:00 valCCC 37.000
2015-09-24_10:00:00 valDDD 37.000
2015-09-24_10:00:00 valEEE 37.000
2015-09-24_10:00:00 valFFF 37.000
2015-09-24_13:30:00 valAAA 40.000
2015-09-24_13:30:00 valBBB 40.000
2015-09-24_13:30:00 valCCC 41.000
2015-09-24_13:30:00 valDDD 42.000
2015-09-24_13:30:00 valEEE 42.000
2015-09-24_13:30:00 valFFF 42.000
2015-09-25_02:00:00 valAAA 5.000
2015-09-25_02:00:00 valBBB 5.000
2015-09-25_02:00:00 valCCC 5.000
2015-09-25_02:00:00 valDDD 5.000
2015-09-25_02:00:00 valEEE 5.000
2015-09-25_02:00:00 valFFF 5.000
2015-09-25_03:30:00 valAAA 15.000
2015-09-25_03:30:00 valBBB 15.000
2015-09-25_03:30:00 valCCC 16.000
2015-09-25_03:30:00 valDDD 16.000
2015-09-25_03:30:00 valEEE 15.000
2015-09-25_03:30:00 valFFF 15.000
2015-09-25_05:30:00 valAAA 19.000
2015-09-25_05:30:00 valBBB 19.000
2015-09-25_05:30:00 valCCC 19.000
2015-09-25_05:30:00 valDDD 20.000
2015-09-25_05:30:00 valEEE 19.000
2015-09-25_05:30:00 valFFF 19.000
2015-09-25_06:00:00 valAAA 19.000
2015-09-25_06:00:00 valBBB 19.000
2015-09-25_06:00:00 valCCC 18.000
2015-09-25_06:00:00 valDDD 19.000
2015-09-25_06:00:00 valEEE 19.000
2015-09-25_06:00:00 valFFF 20.000
References :
  • Gnuplot terciary condition:
http://stackoverflow.com/questions/6564561/gnuplot-conditional-plotting-plot-col-acol-b-if-col-c-x
  • Colors
 http://gnuplot.sourceforge.net/demo/rainbow.html