topic Re: Counting in loop in Python Questions

Counting in loop

Mick — Sun, 18 Apr 2021 09:05:53 GMT

Good day everybody,

I am currently working with a feature class. I have a field with each cat that could be repeated around 100 or more times. However, I have 25 different cats.

My task is to count how many times each cat appears in the field. Currently, I have a total number 40000 when I use "numbermyList = len(myList)" after my loop and only one when I use it in the loop. When I use "numbermyList = len(cat)", it gives the total number only for the first cat but not working the other cats.(If i use inside or outside of the loop)

Could you please recommend to me how to use the loop to count the number of each cat in my field?

Certainly, I would like to use the received number in my next loop, so I will receive something like this: 1st cat = 4000(numbermyList = len(myList)), 2sd cat 5000 and so on (numbermyList = len(myList)).

Re: Counting in loop

BlakeTerhune — Wed, 14 Apr 2021 14:40:52 GMT

You can use a default dictionary for this!

from collections import defaultdict fakeCursor = ["one", "three", "two", "one", "one", "two", "five", "nine"] counter = defaultdict(int) for i in fakeCursor: counter[i] += 1 print counter

Output:

defaultdict(<type 'int'>, {'nine': 1, 'five': 1, 'three': 1, 'two': 2, 'one': 3})

Re: Counting in loop

jcarlson — Wed, 14 Apr 2021 14:41:34 GMT

Can you elaborate a bit on this? Do you mean you want the count of occurrences per cat, something like:

cat 1: 100
cat 2: 2500
etc...

I think part of the problem here is that the myList object is being redefined as an empty list for every iteration.

Re: Counting in loop

JoshuaBixby — Wed, 14 Apr 2021 14:52:41 GMT

Since there is a bit of confusion over what you are trying to do within your loop, I suggest you step back from tools and solutions and explain a bit what your requirement is, i.e., just describe what you are trying to achieve overall.

Re: Counting in loop

JohannesLindner — Wed, 14 Apr 2021 15:07:54 GMT

cat_names = ["cat_1", "cat_2", "cat_3", "cat_25"] cat_numbers = [] for name in cat_names: sql_query = "CatName = '{}'".format(name) cat_rows = [c for c in arcpy.da.SearchCursor("Cat_Layer", ["CatName"], sql_query)] cat_numbers.append(len(cat_rows)) for name, number in zip(cat_names, cat_numbers): print("{} appeared {} times in Cat_Layer.".format(name, number)) #cat_1 appeared 56 times in Cat_Layer. #... #cat_25 appeared 572 times in Cat_Layer.

Re: Counting in loop

BlakeTerhune — Wed, 14 Apr 2021 15:23:41 GMT

Do you have other CatName values in Cat_Layer that aren't in cat_names? In other words, do you want to count all occurrences of every CatName value or only the ones you explicitly define?

Re: Counting in loop

JohannesLindner — Thu, 15 Apr 2021 05:38:55 GMT

Good question. In that case, you would run this before:

cat_names = [c[0] for c in arcpy.da.SearchCursor("Cat_Layer", ["CatName"])] cat_names = list(set(cat_names)) # names of all cats in Cat_Layer