How to use multiple sync.WaitGroup in a single program - go

Question

In my Go program I start multiple worker groups for every department.
I want to wait for workers from each department to complete before exiting the program
I cannot use a single WaitGroups because in the actual scenario I may have to end any particular department and need to wait only on that.
This is simplified version of code, but it panics with a message
panic: runtime error: invalid memory address or nil pointer dereference
package main
import (
"fmt"
"sync"
"time"
)
var wgMap map[string]*sync.WaitGroup
func deptWorker(dName string, id int) {
defer wgMap[dName].Done()
fmt.Printf("Department %s : Worker %d starting\n", dName, id)
time.Sleep(time.Second)
fmt.Printf("Department %s : Worker %d done\n", dName, id)
}
func department(dName string) {
var wg sync.WaitGroup
for i := 1; i <= 3; i++ {
wg.Add(1)
go deptWorker(dName, i)
}
wgMap[dName] = &wg
}
func main() {
go department("medical")
go department("electronics")
wgMap["medical"].Wait()
wgMap["electronics"].Wait()
}

Answer 1

Two fix nil panic you simply need to use
var wgMap = map[string]*sync.WaitGroup{}
It will initialize the map. However, in my view, it's better here to create a new abstraction, let's name it 'WaitMap'.
It can be implemented in this way:
package main
import (
"fmt"
"sync"
"time"
)
type WaitMapObject struct {
wg map[string]int
mu sync.Mutex
cond sync.Cond
}
func WaitMap() *WaitMapObject {
m := &WaitMapObject{}
m.wg = make(map[string]int)
m.cond.L = &m.mu
return m
}
func (m *WaitMapObject) Wait(name string) {
m.mu.Lock()
for m.wg[name] != 0 {
m.cond.Wait()
}
m.mu.Unlock()
}
func (m *WaitMapObject) Done(name string) {
m.mu.Lock()
no := m.wg[name] - 1
if no < 0 {
panic("")
}
m.wg[name] = no
m.mu.Unlock()
m.cond.Broadcast()
}
func (m *WaitMapObject) Add(name string, no int) {
m.mu.Lock()
m.wg[name] = m.wg[name] + no
m.mu.Unlock()
}
func deptWorker(dName string, id int, wm *WaitMapObject) {
defer wm.Done(dName)
fmt.Printf("Department %s : Worker %d starting\n", dName, id)
time.Sleep(time.Second)
fmt.Printf("Department %s : Worker %d done\n", dName, id)
}
func department(dName string, wm *WaitMapObject) {
for i := 1; i <= 3; i++ {
wm.Add(dName,1)
go deptWorker(dName, i, wm)
}
wm.Done(dName)
}
func main() {
wm := WaitMap()
wm.Add("mediacal",1)
go department("medical", wm)
wm.Add("electronics",1)
go department("electronics", wm)
wm.Wait("medical")
wm.Wait("electronics")
}