script to edit and save statistics from raster maps in GRASS GIS, using r.stats

calc_stats.py

# import modules
import grass.script as grass

def export_statistics(input_map = ''):
	'''
	Function to calculate and export statistics (using r.stats) from landscape metrics maps.
	Results are given in hectares.
		
	Parameters
	----------
	input_map: string
		Landscape metric map from which statistics will be calculated.

	Returns
	-------
	out: txt file
		File with the id of the patch (or class), the area (or correspondent metric), in hectares,
		and the percentage of the total each patch correponds.
	'''

	# Define region
  	grass.run_command('g.region', rast=input_map)  
  	# Calculate area and percentage statistics for the input map using r.stats
  	x = grass.read_command('r.stats', flags = 'nap', input = input_map)
  	
  	# Separating values by line
  	y = x.split('\n')
	
  	# Initialize arrays
  	idd = []
  	areas = []
  	
  	if len(y) != 0:
    	# For each element in the list of values
    	for i in y:
	      	if i != '':
	    	    ##print i
    	    	# Split by space
	    	    f = i.split(' ')
          		##print f
          		# Get id (raster value)
          		ids = f[0]
          		ids = int(ids)
          		idd.append(ids)
          		##print ids
          		# Get area in m2 and transform to hectares
          		ha = f[1]
          		haint = float(ha)
          		haint = haint/10000
          		areas.append(haint)
          		##print haint
    	      
    	# Calculate the percentage
    	percentages = [float(i)/sum(areas) for i in areas]
    	
    	# Open output file
	    txt_file = open(input_map+'.txt', 'w')
    	
    	# Write header
    	txt_file.write('CODE'+','+'AREA_HA'+','+'PROPORTION\n')    

    	# For each element
    	for i in range(len(idd)):
      		# Write line in the output file
      		txt_file.write(`idd[i]`+','+`areas[i]`+','+`percentages[i]`+'\n')
          	
    	# Close the output file
    	txt_file.close()