[Golang] golangbootcamp 補遺(三) -- Collection Types
閱讀golang bootcamp 筆記補遺。
Array
長度固定, 不能重新更動陣列長度。
但是可以隱性的宣告陣列長度:
package main
import "fmt"
func main() {
a := [...]string{"hello", "world!"}
fmt.Printf("%q", a)
}
Slice
幾乎都用slice取代array。
Slices can be resized since they are just a wrapper on top of another data structure.
Making Slices
可以直接賦值建立slice:
mySlice := []int{2, 3, 5, 7, 11, 13}
或是利用make可以建立特定長度的空slice, 像以下為make([]byte, 5):
more:
func main() {
cities := make([]string, 3)
cities[0] = "Santa Monica"
cities[1] = "Venice"
cities[2] = "Los Angeles"
fmt.Printf("%q", cities)
// ["Santa Monica" "Venice" "Los Angeles"]
}
Appending to a slice
Slice就是一個指向底層陣列的指標, 因此像如下:
func main() {
cities := []string{}
cities[0] = "Santa Monica"
}
會產生runtime error:
panic: runtime error: index out of range
goroutine 1 [running]:
因為我們的cities slice指向的是一個長度為0的空陣列。若要加項目到該種slice, 需要使用append function:
func main() {
cities := []string{}
cities = append(cities, "San Diego", "Mountain View")
fmt.Printf("%q", cities) // ["San Diego" "Mountain View"]
}
也可以利用... 將一個slice加到另外一個slice:
func main() {
cities := []string{"San Diego", "Mountain View"}
otherCities := []string{"Santa Monica", "Venice"}
cities = append(cities, otherCities...)
fmt.Printf("%q\n", cities) // ["San Diego" "Mountain View" "Santa Monica" "Venice"]
fmt.Println(len(countries))
}
...的意思表示該元素為一個collection。要加的slice和被加的slice,其型別必須要相同才行。
利用len function來查看slice的長度。
Nil Slice
func main() {
var z []int
fmt.Println(z, len(z), cap(z)) // [] 0 0
if z == nil {
fmt.Println("nil!")
}
// nil!
}
nil slice長度0, 容量0, nill slice的zero value為 nil。
練習題!
有以下姓名的list, 我需要依照其長度分類切成不同的slice:
package main
var names = []string{"Katrina", "Evan", "Neil", "Adam", "Martin", "Matt",
"Emma", "Isabella", "Emily", "Madison",
"Ava", "Olivia", "Sophia", "Abigail",
"Elizabeth", "Chloe", "Samantha",
"Addison", "Natalie", "Mia", "Alexis"}
func main() {
// insert your code here
}
實作結果應該印出:
[[] [] [Ava Mia] [Evan Neil Adam Matt Emma] [Emily Chloe]
[Martin Olivia Sophia Alexis] [Katrina Madison Abigail Addison Natalie]
[Isabella Samantha] [Elizabeth]]
我的
沒仔細看題目, 我寫的笨解法如下:
package main
import "fmt"
var names = []string{"Katrina", "Evan", "Neil", "Adam", "Martin", "Matt",
"Emma", "Isabella", "Emily", "Madison",
"Ava", "Olivia", "Sophia", "Abigail",
"Elizabeth", "Chloe", "Samantha",
"Addison", "Natalie", "Mia", "Alexis"}
func main() {
var (
name1 = []string{}
name2 = []string{}
name3 = []string{}
name4 = []string{}
name5 = []string{}
name6 = []string{}
name7 = []string{}
name8 = []string{}
name9 = []string{}
)
for _, name := range names {
switch len(name) {
case 1:
name1 = append(name1, name)
case 2:
name2 = append(name2, name)
case 3:
name3 = append(name3, name)
case 4:
name4 = append(name4, name)
case 5:
name5 = append(name5, name)
case 6:
name6 = append(name6, name)
case 7:
name7 = append(name7, name)
case 8:
name8 = append(name8, name)
case 9:
name9 = append(name9, name)
}
}
fmt.Print(name1, name2, name3, name4, name5, name6, name7, name8, name9)
}
解答
package main
import "fmt"
var names = []string{"Katrina", "Evan", "Neil", "Adam", "Martin", "Matt",
"Emma", "Isabella", "Emily", "Madison",
"Ava", "Olivia", "Sophia", "Abigail",
"Elizabeth", "Chloe", "Samantha",
"Addison", "Natalie", "Mia", "Alexis"}
func main() {
var maxLen int
for _, name := range names {
if l := len(name); l > maxLen {
maxLen = l
}
}
output := make([][]string, maxLen)
for _, name := range names {
output[len(name)-1] = append(output[len(name)-1], name)
}
fmt.Printf("%v", output)
}
先抓出該list每個名字最大長度應該是多少, 再來建立一個長度是名字最大長度的二維slice, 再重新range把姓名塞到對應slice元素中去。
Map
建立 map:
package main
import "fmt"
func main() {
celebs := map[string]int{
"AA": 1,
"BB": 3,
"CC": 5,
}
fmt.Println(celebs)
fmt.Printf("%#v", celebs)
}
注意Golang不保證在map裏面key的順序!
注意Printf使用%#v會列印出map的語法:
map[AA:1 BB:3 CC:5]
map[string]int{"CC":5, "AA":1, "BB":3}
如先建立map在賦予該map值, 那就要要用make:
package main
import "fmt"
type Vertex struct {
Lat, Long float64
}
var m map[string]Vertex
func main() {
m = make(map[string]Vertex)
m["Bell Labs"] = Vertex{40.68433, -74.39967}
fmt.Println(m["Bell Labs"])
}
就會列印出:
{40.68433 -74.39967}
Mutating map
刪除一個元素:
delete(m, key)
檢查看該元素是否存在:
elem, ok := m[key]
elem不存在會得到zero value, ok為flase。
Map練習題!
題目:
package main
import (
"code.google.com/p/go-tour/wc"
)
func WordCount(s string) map[string]int {
return map[string]int{"x": 1}
}
func main() {
wc.Test(WordCount)
}
wc.Test會輸入一系列測試字串, 檢查我們給的map成員是否是該字串每個單字總共出現的次數:
f("I am learning Go!") =
map[string]int{"x":1}
want:
map[string]int{"am":1, "learning":1, "Go!":1, "I":1}
提示使用 strings.Fields來實作:
package main
import (
"code.google.com/p/go-tour/wc"
"strings"
)
func WordCount(s string) map[string]int {
words := strings.Fields(s)
count := make(map[string]int{})
for _, word := range words {
count[word]++
}
return count
}
func main() {
wc.Test(WordCount)
}
count[word]++真的是很特別好用的方式阿...
More
Go Slices: usage and internals