Collection functions (length, flatten, merge) in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the number of elements in the list.

Terraform

length = length([1])

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

A[1, 2, 3, 4]

B["apple", "banana", "cherry"]

C[]

D[true, false]

Attempts:

3 left

💡 Hint

Common Mistakes

Using an empty list which returns 0.

Using a non-list value which causes an error.

The length function returns the number of elements in the list. Here, the list has 3 elements.

2fill in blank

medium

Complete the code to flatten a list of lists into a single list.

Terraform

flat_list = flatten([1])

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

A["a", "b", "c"]

B[1, 2, 3, 4]

C[["a"], ["b", "c"]]

D[[1, 2], [3, 4]]

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a flat list which does nothing.

Passing a non-list or empty list.

The flatten function takes a list of lists and combines all inner lists into one single list.

3fill in blank

hard

Fix the error in the merge function to combine two maps correctly.

Terraform

combined = merge([1], {"key2" = "value2"})

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

A["key1" = "value1"]

B["key1", "value1"]

C{"key1" = "value1"}

D{"key1", "value1"}

Attempts:

3 left

💡 Hint

Common Mistakes

Using lists instead of maps.

Using incorrect syntax for maps.

The merge function requires maps as arguments. Option C is a valid map with key-value pairs.

4fill in blank

hard

Fill both blanks to create a map with keys as strings and values as lengths of words longer than 4 characters.

Terraform

result = { [1] : length([2]) for word in words if length(word) > 4 }

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

Aword

C"word"

Dwords

Attempts:

3 left

💡 Hint

Common Mistakes

Using string literals as keys instead of variables.

Using the whole list instead of the single word.

The key should be the variable word itself (not a string literal), and the value is the length of that word.

5fill in blank

hard

Fill all three blanks to create a merged map with uppercase keys and values greater than 3.

Terraform

filtered = { [1] : [2] for k, v in merge(map1, map2) if [3] }

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

Ak.upper()

Bv

Cv > 3

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using original keys without uppercase.

Filtering with wrong conditions.

Swapping keys and values.

The keys are converted to uppercase with k.upper(), values are v, and the filter keeps values greater than 3.

Practice

1. What does the Terraform function length() do when applied to a list?

easy

A. Returns the number of items in the list

B. Combines all items into a single string

C. Flattens nested lists into one list

D. Merges the list with another list

Solution

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

   The length() function counts how many elements are in a list, map, or string.

2. Step 2: Apply to a list context

   When used on a list, it returns the total number of items inside that list.

3. Final Answer:

   Returns the number of items in the list -> Option A

4. Quick Check:

   length(list) = count of items [OK]

Hint: Count items with length() to get list size fast [OK]

Common Mistakes:

• Thinking length() merges lists
• Confusing length() with flatten()
• Assuming length() returns the list itself

2. Which of the following is the correct syntax to merge two maps map1 and map2 in Terraform?

easy

A. length(map1, map2)

B. flatten(map1, map2)

C. map1 + map2

D. merge(map1, map2)

Solution

1. Step 1: Identify the function for combining maps

   The merge() function is used to combine two or more maps into one.

2. Step 2: Check syntax correctness

   The correct syntax is merge(map1, map2). Other options either use wrong functions or invalid operators.

3. Final Answer:

   merge(map1, map2) -> Option D

4. Quick Check:

   merge() combines maps correctly [OK]

Hint: Use merge() with parentheses and commas for maps [OK]

Common Mistakes:

• Using + operator to merge maps
• Confusing flatten() with merge()
• Passing maps without commas

3. What is the output of this Terraform expression?

flatten([["a", "b"], ["c"], ["d", "e"]])

medium

A. [["a", "b"], ["c"], ["d", "e"]]

B. ["a", "b", "c", "d", "e"]

C. ["a", "b", ["c"], "d", "e"]

D. Error: flatten() only works on maps

Solution

1. Step 1: Understand flatten() function

   The flatten() function takes a list of lists and combines all inner lists into one single list.

2. Step 2: Apply flatten() to the given nested list

   Input is [["a", "b"], ["c"], ["d", "e"]]. Flattening merges all inner lists into ["a", "b", "c", "d", "e"].

3. Final Answer:

   ["a", "b", "c", "d", "e"] -> Option B

4. Quick Check:

   flatten(nested list) = single list [OK]

Hint: flatten() removes inner list brackets to one list [OK]

Common Mistakes:

• Thinking flatten() returns original nested list
• Expecting flatten() to work on maps
• Confusing flatten() with merge()

4. Given the code snippet:

locals {
  map1 = { a = 1, b = 2 }
  map2 = { b = 3, c = 4 }
  result = merge(map1, map2)
}

What is the value of local.result?

medium

A. { a = 1, b = 3, c = 4 }

B. { a = 1, b = 2, c = 4 }

C. { a = 1, b = 5, c = 4 }

D. Error: duplicate keys not allowed in merge

Solution

1. Step 1: Understand merge() behavior with duplicate keys

   When keys overlap, the value from the last map argument overrides earlier ones.

2. Step 2: Apply merge to map1 and map2

   map1 has b=2, map2 has b=3. The merged map uses b=3 from map2, so result is { a=1, b=3, c=4 }.

3. Final Answer:

   { a = 1, b = 3, c = 4 } -> Option A

4. Quick Check:

   merge() overrides duplicate keys with last map [OK]

Hint: Last map's keys override earlier ones in merge() [OK]

Common Mistakes:

• Assuming values add up for duplicate keys
• Expecting error on duplicate keys
• Confusing merge() with flatten()

5. You have a list of maps:

list_of_maps = [
  { name = "Alice", age = 30 },
  { name = "Bob", age = 25 },
  { name = "Carol", age = 27 }
]

Which Terraform expression correctly merges all maps into one map with all keys and values combined?

hard

A. length(list_of_maps)

B. flatten(list_of_maps)

C. merge(list_of_maps...)

D. merge(list_of_maps)

Solution

1. Step 1: Understand how to merge multiple maps in a list

   To merge all maps inside a list, you use the splat operator ... to unpack the list as arguments to merge().

2. Step 2: Check each option

   merge(list_of_maps...) uses merge(list_of_maps...) which correctly merges all maps. flatten(list_of_maps) tries flatten on maps (invalid), C returns count, D passes list directly (invalid).

3. Final Answer:

   merge(list_of_maps...) -> Option C

4. Quick Check:

   Use merge() with ... to combine list of maps [OK]

Hint: Use ... to unpack list when merging maps [OK]

Common Mistakes:

• Passing list directly to merge() without ...
• Using flatten() on maps
• Confusing length() with merge()