Deleting map entries in Go - Mini Project: Build & Apply

Deleting map entries

📖 Scenario: You have a map of fruits and their quantities in a store. Sometimes, fruits run out of stock and need to be removed from the map.

🎯 Goal: Learn how to delete entries from a Go map when the quantity is zero.

📋 What You'll Learn

Create a map called inventory with exact fruit names and quantities

Create a variable called threshold set to 0

Use a for loop with variables fruit and quantity to iterate over inventory

Delete entries from inventory where quantity is equal to threshold

Print the final inventory map

💡 Why This Matters

🌍 Real World

Managing inventory data where items with zero stock need to be removed to keep the data clean.

💼 Career

Understanding how to manipulate maps and remove entries is important for backend development, data processing, and managing state in Go applications.

1

Create the initial inventory map

Create a map called inventory with these exact entries: "apple": 5, "banana": 0, "orange": 3, "grape": 0

Go

// Your code here

Hint

Use map[string]int to create a map with string keys and int values.

2

Add a threshold variable

Create an integer variable called threshold and set it to 0

Go

package main

import "fmt"

func main() {
    inventory := map[string]int{"apple": 5, "banana": 0, "orange": 3, "grape": 0}
    // Your code here
}

Hint

Use threshold := 0 to create the variable.

3

Delete entries with quantity equal to threshold

Use a for loop with variables fruit and quantity to iterate over inventory. Inside the loop, delete the entry from inventory if quantity is equal to threshold

Go

package main

import "fmt"

func main() {
    inventory := map[string]int{"apple": 5, "banana": 0, "orange": 3, "grape": 0}
    threshold := 0

    // Use a for loop to delete entries
    // Your code here
}

Hint

Use delete(map, key) to remove an entry from a map.

4

Print the updated inventory

Write fmt.Println(inventory) to display the updated inventory map

Go

package main

import "fmt"

func main() {
    inventory := map[string]int{"apple": 5, "banana": 0, "orange": 3, "grape": 0}
    threshold := 0

    for fruit, quantity := range inventory {
        if quantity == threshold {
            delete(inventory, fruit)
        }
    }

    // Your code here
}

Hint

Use fmt.Println(inventory) to print the map.

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