pandas.DataFrame.drop_duplicates() – Examples

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  • Post last modified:December 2, 2024
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Pandas DataFrame.drop_duplicates() function is used to remove duplicates from the DataFrame rows and columns. When data preprocessing and analysis step, data scientists need to check for any duplicate data is present, if so need to figure out a way to remove the duplicates.

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Key Points –

  • drop_duplicates() is used to remove duplicate rows from a DataFrame.
  • You can specify which columns to check for duplicates using the subset parameter.
  • By default, drop_duplicates() keeps the first occurrence of each duplicate row, but you can change this behavior with the keep parameter (e.g., ‘last’ or False to drop all duplicates).
  • You can drop duplicates based on the index, but this requires setting the subset parameter to include the index.
  • The data types of the remaining rows after dropping duplicates are preserved.
  • drop_duplicates() works with DataFrames that have a MultiIndex, applying the duplicate check on the specified levels.

Syntax of DataFrame.drop_duplicates()

Following is the syntax of the drop_duplicates() function. It takes subset, keep, inplace and ignore_index as params and returns DataFrame with duplicate rows removed based on the parameters passed. If inplace=True is used, it updates the existing DataFrame object and returns None.


# Syntax of DataFrame.drop_duplicates()
DataFrame.drop_duplicates(subset=None, keep='first', inplace=False, ignore_index=False)

Following are the parameters of drop_duplicates.

  • subset – Default is None. Specifies the column(s) to consider for identifying duplicates. If None, it considers all columns.
  • keep –
    • first : Drop duplicates except for the first occurrence.
    • last : Drop duplicates except for the last occurrence.
    • False : Drop all duplicates.inplacebool, default False.
  • inplace – Default is False. If True, the operation is performed in place, and the original DataFrame is modified. If False, a new DataFrame is returned.
  • ignore_index – If True the resulting axis will be labeled 0, 1, …, n – 1.

Considering certain columns is optional. Indexes, including time indexes are ignored. Parameter subset column label or sequence of labels, optional. Only consider certain columns for identifying duplicates, by default use all of the columns. keep{‘first’, ‘last’, False}, and default ‘first’. keep parameter determines which duplicates (if any) to keep.

Whether to drop duplicates in place or to return a copy.ignore_indexbool, default is False. If True means the resulting axis will be labeled 0, 1, …, n – 1.

Drop Duplicates in DataFrame

To run some examples of pandas DataFrame.drop_duplicates() function, let’s create a Pandas DataFrame.


import pandas as pd
technologies = {
    'Courses':["Spark","PySpark","PySpark","Pandas"],
    'Fee' :[20000,22000,22000,30000],
    'Duration':['30days','35days','35days','50days'],
              }
# Create dataframe
df = pd.DataFrame(technologies)
print(df)

Below is the data frame with duplicates.


# Output:
   Courses    Fee Duration
0    Spark  20000   30days
1  PySpark  22000   35days
2  PySpark  22000   35days
3   Pandas  30000   50days

Now applying the drop_duplicates() function on the data frame as shown below, drops the duplicate rows.


# Drop duplicates
df1 = df.drop_duplicates()
print(df1)

Following is the output.


# Output:
   Courses    Fee Duration
0    Spark  20000   30days
1  PySpark  22000   35days
3   Pandas  30000   50days

Drop Duplicates on Selected Columns

Use subset param, to drop duplicates on certain selected columns. This is an optional param. By default, it is None, which means using all of the columns for dropping duplicates.


# Using subset option 
df3 = df.drop_duplicates(subset=['Courses'])
print(df3)


# Output:
   Courses    Fee Duration
0    Spark  20000   30days
1  PySpark  22000   35days
3   Pandas  30000   50days

FAQ on pandas.DataFrame.drop_duplicates()

What does drop_duplicates() do?

The drop_duplicates() function removes rows that are identical to a previous row, keeping the first occurrence by default.

How do I remove duplicates from specific columns?

To remove duplicates from specific columns in a Pandas DataFrame, you can use the drop_duplicates() function with the subset parameter. This allows you to specify which columns to consider when identifying duplicates, while keeping the first or last occurrence of each duplicate.

Can I keep the last occurrence instead of the first?

You can keep the last occurrence instead of the first when removing duplicates in a Pandas DataFrame. To do this, you can use the drop_duplicates() function with the keep='last' argument.

Is the operation in-place?

By default, the drop_duplicates() operation is not in-place, meaning it returns a new DataFrame with the duplicates removed, while leaving the original DataFrame unchanged. If you want to modify the DataFrame in-place (i.e., remove the duplicates directly from the original DataFrame without creating a new one), you can set the inplace parameter to True.

What if my DataFrame has a MultiIndex?

The function works the same way for MultiIndex DataFrames, but you can specify which level(s) of the index you want to consider by using the subset parameter.

Conclusion

In this article, you have learned how to drop/remove/delete duplicates using pandas.DataFrame.drop_duplicates(). And also learned how to use option subset.

Reference

https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.drop_duplicates.html