CODEWITHSUNDEEP
pythonloopscount
Mike
Mike

Reputation: 4435

How do I loop through the rows in a column and count them using Python?

I am trying to loop through column in an access table using Python. The column I have is sorted ascending.

I am trying to loop though the rows and when the value in the column changes, I want to get count of of all those values. In the example column below, the first group of values I want to count are the M1's. When the next row changes to M21, I want to count the M21's until it changes to M23b and so on.

I don't want to use an if/else statement, because there are a few hundred different possible values. I played around with the groupby function in the itertools module, but I haven't been able to solve the syntax to work in my example. I also tried a silly loop doing something like if row != row.next(): do_something but that blew up in my face. If anyone can suggest a work-around or show me a sample script that will do this for me, I'd appreciate it.

Example Column:

M1
M1
M1
M21
M21
M23b
M23b
S2
S23b
S23B
O1
O2
O2
O2

Upvotes: 2

Views: 6124

Answers (2)

Ethan Furman
Ethan Furman

Reputation: 69240

If you want to add printing in a loop doing other work, the following may be helpful:

from collections import Counter  # or defaultdict

col_counts = Counter()           # or defaultdict(int)

last_value = object()            # won't show up in table
for row in access_table:
    col_counts[row[field]] += 1
    if row[field] != last_value:
        print(col_counts[last_value])
        last_value = row[field]
    ...
    other_processing()
    ...

Upvotes: 1

agf
agf

Reputation: 176950

Your intuition to use itertools.groupby was correct:

for key, group in groupby(column):
    count = sum(1 for item in group) # Thanks JBernardo
    # the key is what is in the column, count is the number of items

Alternatively, if all you need is the counts, it's as simple as:

from collections import Counter # Python 2.7+

group_counts = Counter(column)

You can implement Counter as:

from collections import defaultdict:

group_counts = defaultdict(int)

for item in column:
    group_counts[item] += 1

on older versions of Python.

Upvotes: 4

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