How to Find Top N Values in pandas DataFrame or Series

Use the nlargest(n) method on a pandas Series or DataFrame column to find the top n values. For DataFrames, specify the column name with nlargest(n, 'column_name') to get rows with the highest values in that column.

Syntax

The nlargest() method is used to get the top n values from a pandas Series or DataFrame.

• Series.nlargest(n): Returns the top n values from a Series.
• DataFrame.nlargest(n, columns): Returns the top n rows ordered by the specified column.

Parameters:

• n: Number of top values to return.
• columns: Column name to sort by (only for DataFrame).

python

series.nlargest(n)
dataframe.nlargest(n, 'column_name')

Example

This example shows how to find the top 3 values in a pandas Series and the top 2 rows with the highest values in a DataFrame column.

python

import pandas as pd

# Create a Series
series = pd.Series([10, 50, 30, 20, 40])

# Find top 3 values in Series
top3_series = series.nlargest(3)

# Create a DataFrame
data = {'name': ['Alice', 'Bob', 'Charlie', 'David'], 'score': [85, 92, 88, 91]}
df = pd.DataFrame(data)

# Find top 2 rows by 'score'
top2_df = df.nlargest(2, 'score')

print('Top 3 values in Series:')
print(top3_series)
print('\nTop 2 rows in DataFrame by score:')
print(top2_df)

Output

Top 3 values in Series:
1    50
4    40
2    30
dtype: int64

Top 2 rows in DataFrame by score:
    name  score
1    Bob     92
3  David     91

Common Pitfalls

Common mistakes when using nlargest() include:

• Not specifying the column name when using it on a DataFrame, which causes an error.
• Using sort_values() instead of nlargest() which is less efficient for large data.
• Confusing nlargest() with head(), which just returns the first rows without sorting.

python

import pandas as pd

data = {'name': ['Alice', 'Bob'], 'score': [85, 92]}
df = pd.DataFrame(data)

# Wrong: missing column name
# df.nlargest(1)  # This will raise TypeError

# Right:
top = df.nlargest(1, 'score')
print(top)

Output

   name  score
1   Bob     92

Quick Reference

Method	Description	Usage Example
Series.nlargest(n)	Get top n values from a Series	series.nlargest(3)
DataFrame.nlargest(n, columns)	Get top n rows by column value	df.nlargest(2, 'score')

Key Takeaways

Use pandas' nlargest() method to efficiently find top n values in Series or DataFrame columns.

Always specify the column name when using nlargest() on a DataFrame.

nlargest() is faster and clearer than sorting and slicing for top values.

Avoid calling nlargest() on a DataFrame without a column name to prevent errors.