Q:

plotting multi bar graph (like clustered column in Excel)

I have the data in the following format 
Type Sub-type Value
A     A_1       10
A     A_1       20
A     A_1       30
A     A_1       40
A     A_2       25
A     A_2       35
A     A_3       45
B     B_1       10
B     B_1       20
B     B_2       30
C     C_1       10
C     C_1       20
C     C_2       10
C     C_2       20 

I want to plot multi bar plot in such a way that the bars of same sub-type will be same color. The different sub-types should have different column. The types should be separated by some spaces.
[Edited]
I used the http://bl.ocks.org/mbostock/3887051 with data.csv file but with some more rows
CA,2704659,4499890,2159981,3853788,10604510,8819342,4114496
CA,3704659,4499890,2659981,3853788,10604510,8819342,4114496
CA,6704659,4499890,2159981,3853788,10604510,8819342,4114496
TX,2027307,3277946,1420518,2454721,7017731,5656528,2472223
NY,1208495,2141490,1058031,1999120,5355235,5120254,2607672
NY,1008495,2671490,1058031,1999120,5355235,5120254,2607672
NY,1208495,2141490,1058031,1999120,5355235,5120254,2607672
FL,1140516,1938695,925060,1607297,4782119,4746856,3187797
IL,894368,1558919,725973,1311479,3596343,3239173,1575308
PA,737462,1345341,679201,1203944,3157759,3414001,1910571
PA,737462,1345341,679201,1203944,3157759,3414001,1910571
PA,37462,345341,79201,3944,31579,34101,1910571

A:

This is too broad a question and the problem is not clearly stated. In order to get you started, here a very basic gnuplot solution (so.dat is the file with the data you have provided):
set datafile separator ","
set style fill solid
set style histogram
set style data histograms
set boxwidth .9
set yrange [0:11000000]
plot "so.dat" u 2:xtic(1), "so.dat" u 3:xtic(1), "so.dat" u 4:xtic(1), "so.dat" u 5:xtic(1), "so.dat" u 6:xtic(1), "so.dat" u 7:xtic(1), "so.dat" u 8:xtic(1)

which produces

You could customize from here, if that is close enough to what you want.

