"subset1","close","43","20"
"subset1","open","53","40"
"subset1","partial","44","28"
"subset2","close","24","31",
"subset2","open","47","35",
"subset2","partial","44","28",
Gnuplot
set datafile separator ","
set style data histogram
set style histogram rowstack gap 1
set style fill solid border -1
set boxwidth 0.5 relative
set xtics rotate by 45 offset -0.8,-4.3
set xlabel offset 0, -2
set bmargin 8
plot \
newhistogram "subset1" lt 1,\
'subset1.csv' using 3:xticlabels(2) title "internal" linecolor rgb "gray",\
'subset1.csv' using 4:xticlabels(2) title "external" linecolor rgb "white",\
newhistogram "subset2" lt 1,\
'subset2.csv' using 3:xticlabels(2) title "" linecolor rgb "gray",\
'subset2.csv' using 4:xticlabels(2) title "" linecolor rgb "white"
gnuplot http://oi61.tinypic.com/nyxoh.jpg