Question

This is probably a simple question, but it’s driving me crazy! I have a python code that performs cellular automata on a land use grid. I’ve made a dictionary of cell id: land use code imported from a text file. I’ve also import of the adjacent neighbors of each cell from a text file. For each cell in the nested loop, I pick out the highest value, count the highest value of the neighboring cells. If this value is greater than the processing cell and occurred more than 4 times, then I update the dictionary for that cell id. The land use codes are ranked in priority. You will see < 6 in the code below…6 is water and wetlands which I do not want to be changed. The first time I run the code, 7509 cells changed land use based on adjacent neighbors land uses. I can comment out the reading the dictionary text file and run it again, then around 5,000 cells changed. Run it again, then even less and so on. What I would like to do is run this in a loop until only 0.0001 of the total cells change, after that break the loop.

I’ve tried several times using iterators like “for r in range(999)—something big; If End_Sim > count: break”. But it breaks after the first one, because the count goes back to zero. I’ve tried putting the count = 0 inside the loop and it adds up…I want it to start back over every time so the number of cells gets less and less. I’m stump…hopefully this is trivial to somebody!

Here’s my code (it’s a clean slate…I’ve deleted my failed attempts to create the number of simulations loop):

import sys, string, csv

#Creating a dictionary of FID: LU_Codes from external txt file
text_file = open("H:\SWAT\NC\FID_Whole_Copy.txt", "rb")
#Lines = text_file.readlines()
FID_GC_dict =  dict()
reader = csv.reader(text_file, delimiter='\t')
for line in reader:
    FID_GC_dict[line[0]] = int(line[1])
text_file.close()

#Importing neighbor list file for each FID value
Neighbors_file = open("H:\SWAT\NC\Pro_NL_Copy.txt","rb")
Entries = Neighbors_file.readlines()
Neighbors_file.close()

Neighbors_List = map(string.split, Entries)

#print Neighbors_List

#creates a list of the current FID
FID = [x[0] for x in Neighbors_List]

#Calculate when to end of one sweep
Tot_Cells = len(FID)
End_Sim = int(0.0001*Tot_Cells)

gridList = []
for nlist in Neighbors_List:
   row = []
   for item in nlist:
       row.append(FID_GC_dict[item])
   gridList.append(row)
#print gridList

#Performs cellular automata rules on land use grid codes

i = iter(FID)
count = 0
for glist in gridList:
    Cur_FID = i.next()
    Cur_GC = glist[0]
    glist.sort()
    lr_Value = glist[-1]
    if lr_Value < 6:
        tie_LR = glist.count(lr_Value)
        if tie_LR >= 4 and lr_Value > Cur_GC:
           FID_GC_dict[Cur_FID] = lr_Value
           #print "The updated gridcode for FID ", Cur_FID, "is ", FID_GC_dict[Cur_FID]
           count += 1
print count

Thanks for any help!

Answer 1

use a while loop:

cnt_total = 1234 # init appropriately
cnt_changed = cnt_total
p = 0.001

while (cnt_changed  > cnt_total*p):
  # your code here
  # remember to update the cnt_changed variable