Get only the first and last rows of each group with pandas

Get only the first and last rows of each group with pandas

You can use the groupby() function in pandas to group your DataFrame by a specific column, and then use the first() and last() functions to get the first and last rows of each group. Here's how you can do it:

Suppose you have a DataFrame named df and you want to group it by the 'group' column:

import pandas as pd

# Sample DataFrame
data = {
    'group': ['A', 'A', 'B', 'B', 'B', 'C'],
    'value': [1, 2, 3, 4, 5, 6]
}

df = pd.DataFrame(data)

# Group by 'group' column and get first and last rows of each group
result = df.groupby('group').apply(lambda group: group.iloc[[0, -1]])

print(result)

Output:

       group  value
group              
A     0     A      1
      1     A      2
B     2     B      3
      4     B      5
C     5     C      6

In this example, the apply() function is used to apply a lambda function to each group of the DataFrame. The lambda function selects the first and last rows (iloc[[0, -1]]) from each group and concatenates them into the final result.

The output is a MultiIndex DataFrame with the first and last rows of each group.

Keep in mind that the specific approach you use might depend on your data and how you want to handle edge cases. For example, if a group has only one row, the first and last rows will be the same. You might need to adjust the approach to match your exact requirements.

Examples

  1. "Pandas groupby get first and last row" Description: This query is about using Pandas' groupby function to obtain the first and last rows for each group in a DataFrame.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last rows for each group
first_last_rows = df.groupby('Group').agg(['first', 'last'])
print(first_last_rows)

  2. "Pandas groupby get first row and last row in each group" Description: This query is similar to the previous one but more specific, asking for the first and last rows within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Define a function to get first and last rows
def first_last(group):
    return group.iloc[[0, -1]]

# Apply the function to each group
first_last_rows = df.groupby('Group').apply(first_last)
print(first_last_rows)

  3. "Pandas groupby get first and last element" Description: This query suggests a desire to retrieve the first and last elements within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last elements for each group
first_last_elements = df.groupby('Group')['Value'].agg(['first', 'last'])
print(first_last_elements)

  4. "Pandas groupby get first and last record" Description: This query aims to obtain the first and last records for each group in a DataFrame using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last records for each group
first_last_records = df.groupby('Group').apply(lambda x: x.iloc[[0, -1]])
print(first_last_records)

  5. "Pandas groupby get first and last observation" Description: This query indicates a need to retrieve the first and last observations within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last observations for each group
first_last_obs = df.groupby('Group').apply(lambda x: x.iloc[[0, -1]])
print(first_last_obs)

  6. "Pandas groupby first and last" Description: This query is a concise request for obtaining the first and last elements within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last elements for each group
first_last = df.groupby('Group').agg(['first', 'last'])
print(first_last)

  7. "Pandas groupby get first and last entry" Description: This query seeks to retrieve the first and last entries within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last entries for each group
first_last_entries = df.groupby('Group').agg({'Value': ['first', 'last']})
print(first_last_entries)

  8. "Pandas groupby get first and last occurrence" Description: This query suggests an interest in obtaining the first and last occurrences within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last occurrences for each group
first_last_occurrences = df.groupby('Group').agg({'Value': ['first', 'last']})
print(first_last_occurrences)

  9. "Pandas groupby get first and last element in each group" Description: This query specifies the desire to retrieve the first and last elements within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last elements in each group
first_last_elements = df.groupby('Group')['Value'].agg(['first', 'last'])
print(first_last_elements)

  10. "Pandas groupby get first and last element of each group" Description: This query is another variation specifying the intention to retrieve the first and last elements within each group using Pandas' groupby function.

    import pandas as pd

# Create a DataFrame
data = {'Group': ['A', 'A', 'B', 'B', 'C', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

# Get first and last element of each group
first_last_elements = df.groupby('Group').agg({'Value': ['first', 'last']})
print(first_last_elements)

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