Memory usage analysis in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the memory_usage() method in pandas do?

It shows the amount of memory used by each column in a DataFrame or by a Series. This helps understand how much space your data takes in memory.

intermediate

How can you get the total memory usage of a pandas DataFrame including the index?

Use df.memory_usage(deep=True).sum(). The deep=True option counts the actual memory usage of objects like strings.

beginner

Why is it useful to analyze memory usage in pandas?

It helps you find which columns use the most memory. Then you can optimize data types or drop unnecessary columns to save memory and speed up your program.

intermediate

What does the deep=True parameter do in memory_usage()?

It makes pandas calculate the full memory usage of object types like strings, not just the pointer size. This gives a more accurate memory size.

intermediate

How can you reduce memory usage after analyzing it in pandas?

You can convert columns to smaller data types (like int8 instead of int64), or convert strings to categories if they have few unique values.

Which pandas method shows memory usage of each column in a DataFrame?

A memory_usage()

B info()

C describe()

D head()

memory_usage() returns memory used by each column. info() shows summary but less detail on memory.

What does setting deep=True in memory_usage() do?

A Ignores index memory

B Compresses data in memory

C Only counts numeric columns

D Counts full memory of object types like strings

With deep=True, pandas counts actual memory used by objects like strings, not just pointers.

How do you get total memory usage of a DataFrame including index?

A df.info()

B df.memory_usage(deep=True).sum()

C df.describe()

D df.head()

Summing memory_usage(deep=True) gives total memory including index.

Why might you convert a string column to category after memory analysis?

A To make it numeric

B To increase memory usage

C To save memory if few unique values

D To delete the column

Categorical data uses less memory when there are few unique values.

Which data type change can reduce memory usage for integer columns?

A int64 to int8

B int8 to int64

C float64 to object

D object to string

Using smaller integer types like int8 reduces memory compared to int64.

Explain how to check memory usage of a pandas DataFrame and why it is important.

Think about how much space your data takes and how to find it.

Describe two ways to reduce memory usage in pandas after analyzing it.

Focus on changing data types and removing data.

Practice

1. What does the memory_usage() function in pandas primarily show?

easy

A. The amount of memory used by each column and the index in a DataFrame

B. The total number of rows in a DataFrame

C. The data types of each column in a DataFrame

D. The number of missing values in each column

Solution

1. Step 1: Understand the purpose of memory_usage()

   This function reports memory consumption of each column and the index in a pandas DataFrame.

2. Step 2: Compare with other options

   Options A, B, and D describe different DataFrame properties unrelated to memory usage.

3. Final Answer:

   The amount of memory used by each column and the index in a DataFrame -> Option A

4. Quick Check:

   memory_usage() = memory per column and index [OK]

Hint: memory_usage() shows memory per column and index [OK]

Common Mistakes:

• Confusing memory_usage() with shape or info()
• Thinking it shows data types or missing values
• Ignoring that it includes index memory

2. Which of the following is the correct syntax to get detailed memory usage of a DataFrame df including object types?

easy

A. df.memory_usage()

B. df.memory_usage(True)

C. df.memory_usage(deep=True)

D. df.memory_usage(deep=False)

Solution

1. Step 1: Recall the parameter for detailed memory info

   The deep=True argument tells pandas to include full memory usage for object columns.

2. Step 2: Check syntax correctness

   df.memory_usage(deep=True) uses the correct keyword argument deep=True. df.memory_usage(True) uses positional argument incorrectly. Options A, B, and C do not provide detailed memory info.

3. Final Answer:

   df.memory_usage(deep=True) -> Option C

4. Quick Check:

   Use deep=True for detailed memory [OK]

Hint: Use deep=True to get full memory info on objects [OK]

Common Mistakes:

• Passing True without keyword (positional argument error)
• Not using deep=True and missing object memory
• Using deep=False which is default and less detailed

3. Given the following code:

import pandas as pd

df = pd.DataFrame({
    'A': [1, 2, 3],
    'B': ['x', 'y', 'z']
})
print(df.memory_usage(deep=True))

What will be the output type of print(df.memory_usage(deep=True))?

medium

A. A pandas Series showing memory usage per column and index

B. A single integer showing total memory usage

C. A dictionary with column names as keys and memory usage as values

D. A DataFrame with memory usage details

Solution

1. Step 1: Understand the return type of memory_usage()

   The memory_usage() method returns a pandas Series with index as column names plus the index, and values as memory usage in bytes.

2. Step 2: Check the code output type

   Since deep=True is used, it includes detailed memory for object columns but still returns a Series, not a dict or DataFrame.

3. Final Answer:

   A pandas Series showing memory usage per column and index -> Option A

4. Quick Check:

   memory_usage() returns Series [OK]

Hint: memory_usage() returns Series with memory per column [OK]

Common Mistakes:

• Expecting total memory as single integer
• Thinking it returns a dictionary or DataFrame
• Confusing output type with other pandas methods

4. You run df.memory_usage(deep=True) but get an error: TypeError: memory_usage() got an unexpected keyword argument 'deep'. What is the likely cause?

medium

A. You forgot to import pandas as pd

B. You are using an older pandas version that does not support the 'deep' argument

C. You passed 'deep' as a positional argument instead of keyword

D. The DataFrame is empty

Solution

1. Step 1: Analyze the error message

   The error says 'unexpected keyword argument deep', meaning the function does not recognize 'deep'.

2. Step 2: Identify cause based on pandas version

   Older pandas versions did not support the 'deep' argument in memory_usage(). This is the most common cause.

3. Final Answer:

   You are using an older pandas version that does not support the 'deep' argument -> Option B

4. Quick Check:

   Old pandas versions lack deep argument [OK]

Hint: Check pandas version if 'deep' argument causes error [OK]

Common Mistakes:

• Assuming import error causes this
• Thinking positional argument fixes it
• Blaming empty DataFrame for this error

5. You have a large DataFrame with many object columns. You want to reduce memory usage by converting some columns to categorical type. Which approach helps you analyze memory before and after conversion?

hard

A. Use df.memory_usage() without deep argument before conversion

B. Use df.info() only after conversion

C. Use df.describe() before conversion

D. Use df.memory_usage(deep=True) before and after converting columns to 'category' dtype

Solution

1. Step 1: Understand memory usage measurement

   Using memory_usage(deep=True) gives detailed memory info including object columns, which is important before conversion.

2. Step 2: Compare memory before and after conversion

   By running this method before and after converting columns to 'category', you can see the memory savings clearly.

3. Final Answer:

   Use df.memory_usage(deep=True) before and after converting columns to 'category' dtype -> Option D

4. Quick Check:

   memory_usage(deep=True) shows detailed memory changes [OK]

Hint: Compare memory_usage(deep=True) before and after changes [OK]

Common Mistakes:

• Using info() which shows less detailed memory
• Using describe() which summarizes stats, not memory
• Using memory_usage() without deep misses object memory