How to duplicate rows of a DataFrame based on values of a specific column?

Question

I have the following DataFrame df:

d = {'1': ['25', 'AAA', 2], '2': ['30', 'BBB', 3], '3': ['5', 'CCC', 2], \
     '4': ['300', 'DDD', 2], '5': ['30', 'DDD', 3],  '6': ['100', 'AAA', 3]}

columns=['Price', 'Name', 'Class']

df = pd.DataFrame.from_dict(data=d, orient='index')
df.columns = columns

I want to duplicate rows based on values of the column Class. In particular, I want to randomly select rows where Class is equal to 3, and duplicate them. For example, in current df I have 3 rows with Class equal to 3. How can I create N duplicates, where N is configurable, for example:

N = 2
target_column = "Class"
target_value = 3
new_df = create_duplicates(df, target_column, target_value, N)

I was thinking to use for-loop and at each iteration (when Class is equal to 3) generate a random number. If it's greater than 0.5, then the row is added to a list of selected rows. This process continues until a list of selected rows contains N rows. Then these N rows are appended to df.

Is there a more elegant and shorter way to do the same? Maybe some built-in pandas functions?

I'm not following your question. Do you want to duplicate the entire dataset by a number N? or just some specific classes? — Quang Hoang
– Quang Hoang, Commented Dec 3, 2019 at 20:33
@QuangHoang: Sorry if it's unclear. I want to duplicate specific rows by a number N. The "specific" rows are those ones that have Class equal to 3. — Fluxy
– Fluxy, Commented Dec 3, 2019 at 20:44

Lukas Thaler · Accepted Answer · 2019-12-03 20:46:58Z

1

I think this script below will do what you need. I lifted the repetition part from: Repeat Rows in Data Frame n Times

n=3
pd.concat([df,df[df['Class']==3].loc[df.index.repeat(n)].dropna()]).sort_values('Name')

edited Dec 3, 2019 at 20:46

Lukas Thaler

2,7205 gold badges19 silver badges35 bronze badges

answered Dec 3, 2019 at 20:37

james hendricks

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2 Comments

Fluxy Over a year ago

Thanks! How does it select rows? Randomly? Or does it take a first row and duplicate it N times?

james hendricks Over a year ago

In this case it selects the rows with a class = 3. Can you better define what you mean by randomly? You could select one row by index, randomly; you could select N rows by index, but you might end up randomly selecting the same row more than one, so you could put some controls around that; you could randomly select a "class" and duplicate all the rows with the select class.

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