Python 按数组列分组，按行号分区

Question

I have an array as below

[('test1@test.com', '220104'), ('test2@test.com', '220104'), ('test3@test.com', '220106'), ('test4@test.com', '220106')]

Here the email ID will be always unique. But the date may come same. The date format will be always YYMMDD. So, the number will change once the date changes

I need output in short as below. The third column basically represents the number of emails of that day

'test1@test.com', '220104', 1
'test2@test.com', '220104', 2
'test3@test.com', '220106', 1
'test4@test.com', '220106', 2

so if the 5th email come, on the same date as the 6th then the output will be

'test1@test.com', '220104', 1
'test2@test.com', '220104', 2
'test3@test.com', '220106', 1
'test4@test.com', '220106', 2
'test4@test.com', '220106', 3

Answer 1

You can use cumcount here:

df = pd.DataFrame([('test1@test.com', '220104'), ('test2@test.com', '220104'), ('test3@test.com', '220106'), ('test4@test.com', '220106')], columns=['email','date'])
df['date_grouped_index'] = df.groupby('date').cumcount() + 1