[GRASS-user] Computing histograms inline with mapcalc?

[Shaun Walbridge]

Hi All,

We're looking at running a Monte Carlo simulation with our GRASS data, 
and one step I'd like to simplify is making histograms.  Currently we 
use R, but given that our input rasters have millions of cells, it's 
time consuming.  I was thinking that we might be able to use GRASS 
directly, since we're just doing many r.mapcalc calls.

I see histogram.c, and ideally I'd like to just roll a custom r.mapcalc 
which adds its output to a histogram function, then write it out at the 
end of the program. My C chops are poor, but I'm imagining something as 
simple (in Python) as:

hist = {}
values = [0.1, 0.1, 0.2, 3, 5, 3, 0.1, 0.2, 3, 0.1, 0.1]

for v in values:
     if hist.has_key(v):
         hist[v] += 1
     else:
         hist[v] = 1

What would be my best bet for creating this histogram?  Is hacking up my 
own mapcalc function feasible?

thanks for the guidance,
Shaun Walbridge