Count appearances of a value until it changes to another value

Question

I have the following DataFrame:

df = pd.DataFrame([10, 10, 23, 23, 9, 9, 9, 10, 10, 10, 10, 12], columns=[\'values\'])

I want to calculate

Answer 1

itertools.groupby

from itertools import groupby

pd.Series(*zip(*[[len([*v]), k] for k, v in groupby(df['values'])]))

10    2
23    2
9     3
10    4
12    1
dtype: int64

---

It's a generator

def f(x):
  count = 1
  for this, that in zip(x, x[1:]):
    if this == that:
      count += 1
    else:
      yield count, this
      count = 1
  yield count, [*x][-1]

pd.Series(*zip(*f(df['values'])))

10    2
23    2
9     3
10    4
12    1
dtype: int64