map() for element-wise mapping in Data Analysis Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to apply the function str.upper to each element in the list words using map().

Data Analysis Python

words = ['apple', 'banana', 'cherry']
result = list(map([1], words))
print(result)

Drag options to blanks, or click blank then click option'

Aupper

Blambda x: x.lower()

Cstr.upper()

Dstr.upper

Attempts:

3 left

💡 Hint

Common Mistakes

Using str.upper() instead of str.upper.

Passing a string like 'upper' instead of the function.

The map() function requires a function object as the first argument. str.upper is the method reference, while str.upper() calls the method immediately, which is incorrect here.

2fill in blank

medium

Complete the code to convert all numbers in the list nums to strings using map().

Data Analysis Python

nums = [1, 2, 3, 4]
str_nums = list(map([1], nums))
print(str_nums)

Drag options to blanks, or click blank then click option'

Astr

Bfloat

Cint

Dlambda x: x + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using int which does not convert numbers to strings.

Using a lambda that adds 1 instead of converting to string.

The str function converts numbers to strings, which is what we want to apply to each element.

3fill in blank

hard

Fix the error in the code to correctly apply the function abs to each element in the list values using map().

Data Analysis Python

values = [-1, -2, 3]
result = list(map([1], values))
print(result)

Drag options to blanks, or click blank then click option'

Aabs()

Babs

Clambda x: abs(x)

Dabs(x)

Attempts:

3 left

💡 Hint

Common Mistakes

Using abs() which calls the function immediately.

Trying to use abs(x) directly without a lambda.

The map() function needs a function object, so abs without parentheses is correct. abs() calls the function immediately and is incorrect here.

4fill in blank

hard

Fill both blanks to create a list of squares of numbers greater than 3 using map() and filter().

Data Analysis Python

numbers = [1, 2, 3, 4, 5]
filtered = filter([1], numbers)
squares = list(map([2], filtered))
print(squares)

Drag options to blanks, or click blank then click option'

Alambda x: x > 3

Blambda x: x < 3

Clambda x: x**2

Dlambda x: x*2

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong filter condition like x < 3.

Using map function that doubles instead of squares.

The filter() uses a function that returns True for numbers greater than 3. The map() applies the square function to each filtered number.

5fill in blank

hard

Fill all three blanks to create a dictionary mapping each word to its length, but only for words longer than 4 characters, using filter() and dictionary comprehension.

Data Analysis Python

words = ['apple', 'bat', 'carrot', 'dog']
lengths = { [1]: [2] for [3] in filter(lambda word: len(word) > 4, words) }
print(lengths)

Drag options to blanks, or click blank then click option'

Aword

Blen(word)

Dw

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names between filter and comprehension.

Using wrong expressions for keys or values.

The dictionary comprehension uses word as the variable from the filter. The key is the word itself, and the value is its length.

Practice

1. What does the map() function do when applied to a list or a DataFrame column in Python?

easy

A. It applies a function or dictionary to each element, changing them one by one.

B. It sorts the list or column in ascending order.

C. It removes duplicate elements from the list or column.

D. It combines two lists or columns into one.

Solution

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

   The map() function is used to apply a transformation to each element of a list or column.

2. Step 2: Identify what map() changes

   It changes each element individually using a function or dictionary mapping.

3. Final Answer:

   It applies a function or dictionary to each element, changing them one by one. -> Option A

4. Quick Check:

   map() changes elements [OK]

Hint: Remember: map changes each item individually [OK]

Common Mistakes:

• Thinking map sorts data
• Confusing map with removing duplicates
• Assuming map merges lists

2. Which of the following is the correct syntax to use map() with a dictionary to replace values in a list colors = ['red', 'blue', 'green'] with numbers?

easy

A. mapped = list(map(lambda x: {'red':1, 'blue':2}[x], colors))

B. mapped = list(map({'red':1, 'blue':2}, colors))

C. mapped = list(map(colors.map({'red':1, 'blue':2})))

D. mapped = list(map(colors, {'red':1, 'blue':2}))

Solution

1. Step 1: Check the correct order of arguments in map()

   The first argument must be a function, the second is the iterable (list).

2. Step 2: Identify which option uses a function properly

   Only mapped = list(map(lambda x: {'red':1, 'blue':2}[x], colors)) uses a lambda function to map dictionary values to list elements correctly.

3. Final Answer:

   mapped = list(map(lambda x: {'red':1, 'blue':2}[x], colors)) -> Option A

4. Quick Check:

   Function first, iterable second in map() [OK]

Hint: map(func, iterable) always has function first [OK]

Common Mistakes:

• Swapping function and iterable arguments
• Trying to pass dictionary directly as function
• Using map() without a function

3. What is the output of this code?

numbers = [1, 2, 3, 4]
result = list(map(lambda x: x * 2, numbers))
print(result)

medium

A. [1, 4, 9, 16]

B. [1, 2, 3, 4]

C. [0, 2, 4, 6]

D. [2, 4, 6, 8]

Solution

1. Step 1: Understand the lambda function

   The lambda function multiplies each element by 2.

2. Step 2: Apply the function to each element in the list

   1*2=2, 2*2=4, 3*2=6, 4*2=8, so the result is [2, 4, 6, 8].

3. Final Answer:

   [2, 4, 6, 8] -> Option D

4. Quick Check:

   Each number doubled = [2,4,6,8] [OK]

Hint: Multiply each element by 2 mentally [OK]

Common Mistakes:

• Confusing map with filter
• Not applying function to all elements
• Mistaking squares for doubles

4. The code below throws an error. What is the problem?

colors = ['red', 'blue', 'green']
mapping = {'red': 1, 'blue': 2}
result = list(map(mapping, colors))
print(result)

medium

A. The map() function requires three arguments, but only two were given.

B. The list colors contains an invalid value 'green'.

C. You cannot pass a dictionary directly as the function argument in map().

D. The print statement is missing parentheses.

Solution

1. Step 1: Check the map() function arguments

   map() expects a function as the first argument, but a dictionary was passed instead.

2. Step 2: Understand why this causes an error

   A dictionary is not callable, so map() cannot use it as a function.

3. Final Answer:

   You cannot pass a dictionary directly as the function argument in map(). -> Option C

4. Quick Check:

   map() needs a function, not a dict [OK]

Hint: map() first argument must be callable (a function) [OK]

Common Mistakes:

• Thinking dictionary can be used directly as function
• Blaming list contents for error
• Ignoring function argument rules

5. You have a list of fruit names: fruits = ['apple', 'banana', 'cherry', 'date']. You want to replace each fruit with its color using this dictionary: colors = {'apple': 'red', 'banana': 'yellow', 'cherry': 'red'}. Using map(), how can you replace fruits not in the dictionary with the string 'unknown'?

hard

A. Use list(map(colors[x], fruits))

B. Use list(map(lambda x: colors.get(x, 'unknown'), fruits))

C. Use list(map(lambda x: colors[x], fruits))

D. Use list(map(colors.get, fruits))

Solution

1. Step 1: Understand the need for default value

   Since 'date' is not in the dictionary, we need a default value to avoid errors.

2. Step 2: Use dictionary's get() method with default in a lambda

   The lambda function calls colors.get(x, 'unknown') to return the color or 'unknown'.

3. Final Answer:

   list(map(lambda x: colors.get(x, 'unknown'), fruits)) -> Option B

4. Quick Check:

   Use get() with default for missing keys [OK]

Hint: Use dict.get(key, default) inside map lambda [OK]

Common Mistakes:

• Not handling missing keys causing KeyError
• Passing dictionary directly without function
• Using map without default value