Deleting map entries in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete the key "apple" from the map.

Go

m := map[string]int{"apple": 5, "banana": 3}
delete(m, [1])

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

A"banana"

B"apple"

C"orange"

D"grape"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a key that does not exist in the map.

Forgetting to put the key in quotes.

The delete function removes the specified key from the map. Here, we delete the key "apple".

2fill in blank

medium

Complete the code to delete the key stored in variable key from the map.

Go

m := map[string]int{"cat": 1, "dog": 2}
key := "dog"
delete(m, [1])

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

Am

B"dog"

C"cat"

Dkey

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the variable name in quotes, which deletes a literal string key.

Passing the whole map instead of the key.

To delete a key stored in a variable, pass the variable name to delete. Here, key holds "dog".

3fill in blank

hard

Fix the error in the code to delete the key "blue" from the map.

Go

colors := map[string]string{"red": "#FF0000", "blue": "#0000FF"}
delete([1], "blue")

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

Acolor

Bcolors["blue"]

Ccolors

Dcolors[blue]

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a map element instead of the map variable.

Using an undefined variable name.

The delete function requires the map variable as the first argument. Here, the map is colors.

4fill in blank

hard

Fill both blanks to delete keys from the map only if they exist.

Go

m := map[string]int{"x": 10, "y": 20}
if _, ok := m[[1]]; ok {
    delete(m, [2])
}

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

A"x"

B"y"

C"z"

D"w"

Attempts:

3 left

💡 Hint

Common Mistakes

Using different keys in the check and delete.

Checking a key that does not exist.

We check if key "x" exists, then delete it. Both blanks use the same key "x".

5fill in blank

hard

Fill all three blanks to delete keys from the map only if their values are zero.

Go

m := map[string]int{"a": 0, "b": 1, "c": 0}
for k, v := range m {
    if v == [1] {
        delete([2], [3])
    }
}

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

A1

Bm

Ck

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing to 1 instead of 0.

Deleting from a wrong variable.

Using a string "k" instead of the variable k.

We delete keys whose value is zero. So, compare v == 0, delete from map m, key k.

Practice

1. What does the built-in delete function do in Go when used as delete(myMap, key)?

easy

A. Adds a new entry with the specified key to the map.

B. Returns the value associated with the key.

C. Clears all entries from the map.

D. Removes the entry with the specified key from the map if it exists.

Solution

1. Step 1: Understand the delete function purpose

   The delete function is used to remove a key and its value from a map.

2. Step 2: Analyze the effect of delete on the map

   When called as delete(myMap, key), it removes the entry if the key exists; otherwise, it does nothing.

3. Final Answer:

   Removes the entry with the specified key from the map if it exists. -> Option D

4. Quick Check:

   delete removes key from map [OK]

Hint: delete(map, key) removes key entry safely [OK]

Common Mistakes:

• Thinking delete adds or returns values
• Confusing delete with clearing the whole map
• Assuming delete returns a value

2. Which of the following is the correct syntax to delete a key named "user1" from a map called users in Go?

easy

A. delete(users, "user1")

B. users.delete("user1")

C. remove(users, "user1")

D. users.deleteKey("user1")

Solution

1. Step 1: Recall Go's delete syntax

   In Go, the built-in function delete is used as delete(map, key) to remove a key.

2. Step 2: Match the correct syntax

   delete(users, "user1") uses delete(users, "user1"), which is the correct syntax. Other options use methods that do not exist in Go.

3. Final Answer:

   delete(users, "user1") -> Option A

4. Quick Check:

   delete(map, key) syntax correct [OK]

Hint: Use delete(map, key) function, not method calls [OK]

Common Mistakes:

• Using method syntax like map.delete(key)
• Using non-existent functions like remove()
• Confusing with other languages' syntax

3. What will be the output of the following Go code?

m := map[string]int{"a": 1, "b": 2}
delete(m, "a")
fmt.Println(m)

medium

A. map[a:1 b:2]

B. map[b:2]

C. map[]

D. Compilation error

Solution

1. Step 1: Understand initial map content

   The map m initially has two entries: "a":1 and "b":2.

2. Step 2: Effect of delete(m, "a")

   The delete call removes the key "a" and its value from the map, leaving only "b":2.

3. Final Answer:

   map[b:2] -> Option B

4. Quick Check:

   Deleting key "a" removes it from map [OK]

Hint: Deleting key removes it; print shows remaining entries [OK]

Common Mistakes:

• Expecting deleted key to remain
• Thinking delete clears whole map
• Assuming syntax error occurs

4. Consider this Go code snippet:

var m map[string]int
delete(m, "key")
fmt.Println("Done")

What will happen when this code runs?

medium

A. Compilation error because delete cannot be used on nil maps.

B. Runtime panic due to deleting from a nil map.

C. Prints "Done" without error.

D. Deletes the key if it exists, then prints "Done".

Solution

1. Step 1: Understand nil map behavior

   In Go, a nil map behaves like an empty map for reads and deletes; deleting a key from a nil map does nothing and does not panic.

2. Step 2: Analyze the code behavior

   Deleting from a nil map is safe and does not cause runtime panic. The program prints "Done" normally.

3. Final Answer:

   Prints "Done" without error. -> Option C

4. Quick Check:

   Deleting from nil map is safe [OK]

Hint: Deleting from nil map is safe, no panic occurs [OK]

Common Mistakes:

• Assuming runtime panic on deleting from nil map
• Thinking delete causes compilation error
• Confusing nil map with uninitialized map variable

5. You have a map m := map[string]int{"x": 10, "y": 0, "z": -5}. You want to delete all keys whose values are zero or less. Which code snippet correctly deletes these entries?

hard

A. for k, v := range m { if v <= 0 { delete(m, k) } }

B. for k := range m { if m[k] < 0 { delete(m, k) } }

C. for k, v := range m { if v == 0 { delete(m, k) } }

D. for k := range m { if m[k] == 0 { delete(m, k) } }

Solution

1. Step 1: Identify keys with values zero or less

   Keys with values <= 0 are "y" (0) and "z" (-5).

2. Step 2: Choose loop that deletes keys with v <= 0

   for k, v := range m { if v <= 0 { delete(m, k) } } uses for k, v := range m and deletes keys where v <= 0, correctly removing "y" and "z".

3. Step 3: Compare other options

   Options A and C check only for == 0, missing negative values like "z":-5. for k := range m { if m[k] < 0 { delete(m, k) } } checks m[k] < 0, missing zero values like "y":0.

4. Final Answer:

   for k, v := range m { if v <= 0 { delete(m, k) } } -> Option A

5. Quick Check:

   Delete keys with value <= 0 using k,v loop [OK]

Hint: Use for k,v range and delete if v <= 0 [OK]

Common Mistakes:

• Deleting only keys with value == 0, missing negatives
• Using only key without value in loop
• Modifying map incorrectly during iteration