Dataframe add column that counts by column condition

Question

I need to add column to current dataframe from excel file, that counts how many time model from dataframe == 'HIT' or "HITTOP'. I have 2 columns dataframe (Model, HK). HK column contain the HIT or HITTOP strings. Below is the code, i made a counter but it only counts if model have non empty string on HK column. Dataframe have models from many files so it have duplicates thats why i need counter on specific condition.

import pandas as pd

df = pd.read_excel(r'C:\Users\user\Desktop\test\output.xlsx')
df['count'] = df.groupby('Model')['HK'].transform('count') #add the count column that counts non empty strings from HK column

df.to_excel(r'C:\Users\user\Desktop\test\output3.xlsx') #save the output

Sample data:

d = {'Model': ['model1', 'model2',' model1', 'model1', 'model2'], 'HK': ['HITTOP', 'HIT', "HITTOP", '', '']}
df = pd.DataFrame(data=d)
df

    Model   HK
0   model1  HITTOP
1   model2  HIT
2   model1  HITTOP
3   model1  
4   model2  

Desired output:

f = {'Model': ['model1', 'model2',' model1', 'model1', 'model2'], 'HK': ['HITTOP', 'HIT', "HITTOP", '', ''],
          'Count': ['2', '1', "2", '2', '1']}
df = pd.DataFrame(data=f)
df

    Model   HK    Count
0   model1  HITTOP  2
1   model2  HIT     1
2   model1  HITTOP  2
3   model1          2
4   model2      

Answer 1

df = df.fillna('')
df2 = df.groupby('HK').apply
    (lambda x: x.shape[0]).rename('Count').reset_index()

df = df.merge(df2, how='left')

    Model      HK  Count
0  model1  HITTOP      2
1  model2     HIT      1
2  model1  HITTOP      2
3  model1              2
4  model2              2