计算一个值出现在 dataframe 列末尾的频率

Question

I have a dataset

|category|
cat a
cat a
cat b
cat b
cat a
cat b
cat a
cat a
cat a
cat a

I'd like to be able to return the total 4 for cat a that occurs at the end of the dataframe in other words if cat b happens then the count starts over once another cat a is found

Answer 1

df['category'] = np.where(df['category'] == "cat b", df['category'],np.nan)
df['category'].bfill().isna().sum()
>>>4