I have a boolean array in python and I want to do a calculation on the cells where the value is 'true'. Currently I am using a nested for loop to go trough all the cells to find the cells with the true values. However, running the program takes a lot of time. I was wondering wether there is a faster way to do this?
for i in range (0,latstep):
for j in range (0,lonstep):
if coastline[i,j] == True:
...
Thanks for your help!
You might consider using concurrent.map() or similar to process the array elements in parallel. Always assuming there aren't dependencies between
the elements.
Another possibility is maintaining a list of the 'true' values when you initially calculate them:
coastlineCache = []
c = foo()
coastline[i][j] = c
if (c):
coastlineCache.append(c)
// later
for (c in coastlineCache):
process_true_item(c)
If, as you've alluded to above, you need the array indices, cache them as a tuple:
coastlineCache = []
c = foo()
coastline[i][j] = c
if (c):
coastlineCache.append((i, j))
// later
for (c in coastlineCache):
process_true_item(c[0], c[1]) # e.g. (i, j)
You can use nested list comprehensions, each comprehension is slightly faster than a generic for-loop on smaller input sizes:
final_list = [[foo(b) for b in i if b] for i in coastline]
coastline?coastline[i,j]is invalid