Counting in loop

307
6
Jump to solution
04-14-2021 05:57 AM
Mick
by
New Contributor

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)).

 

 

 

 

  

0 Kudos
1 Solution

Accepted Solutions
JohannesLindner
Occasional Contributor III

 

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.

 


Have a great day!
Johannes

View solution in original post

0 Kudos
6 Replies
BlakeTerhune
MVP Regular Contributor

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})

jcarlson
MVP Regular Contributor

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.

- Josh Carlson
Kendall County GIS
0 Kudos
JoshuaBixby
MVP Esteemed Contributor

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.

JohannesLindner
Occasional Contributor III

 

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.

 


Have a great day!
Johannes

View solution in original post

0 Kudos
BlakeTerhune
MVP Regular Contributor

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?

0 Kudos
JohannesLindner
Occasional Contributor III

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

 


Have a great day!
Johannes
0 Kudos