英文:
Check if key exists in multiple maps in one condition
问题
我需要检查两个映射中是否存在相同的键:
if v1, ok1 := map1["aaa"]; ok1 {
...
}
if v2, ok2 := map2["aaa"]; ok2 {
...
}
是否可能将这两个条件合并为一个?我设法做到了这样:
v1, ok1 := map1["aaa"]
v2, ok2 := map2["aaa"]
if ok1 && ok2 {
...
}
但我想知道是否可以在一个 if
条件中完成赋值和检查。
英文:
I need to check if the same key exists in two maps:
if v1, ok1 := map1["aaa"]; ok1 {
...
}
if v2, ok2 := map2["aaa"]; ok2 {
...
}
Is it possible to join these two conditions into one? I managed to do something like this:
v1, ok1 := map1["aaa"]
v2, ok2 := map2["aaa"]
if ok1 && ok2 {
...
}
but I'm curious whether it (assigning and checking) can be done in one if
condition.
答案1
得分: 8
不,这是不可能的。规范:索引表达式:
在特殊形式的赋值或初始化中,对类型为map[K]V
的映射a
进行索引表达式操作,例如:
v, ok = a[x]
v, ok := a[x]
var v, ok = a[x]
会产生一个额外的无类型布尔值。如果键x
存在于映射中,ok
的值为true
,否则为false
。
因此,只有在没有其他赋值操作时,才能使用特殊的v, ok := m[k]
形式。
然而,如果你不使用映射值类型的零值,你可以使用简单的元组赋值来进行检查;通过不使用特殊形式,而是使用两个简单的索引表达式。
例如,如果你的值类型是某个接口类型(例如interface{}
),并且你知道你不使用nil
值,你可以这样做:
if v1, v2 := m1["aaa"], m2["aaa"]; v1 != nil && v2 != nil {
fmt.Printf("Both map contains key 'aaa': %v, %v\n", v1, v2)
}
当然,通过一个辅助函数,你可以一步完成:
func idx(m1, m2 map[string]interface{}, k string) (
v1, v2 interface{}, ok1, ok2 bool) {
v1, ok1 = m1[k]
v2, ok2 = m2[k]
return
}
使用它:
if v1, v2, ok1, ok2 := idx(m1, m2, "aaa"); ok1 && ok2 {
fmt.Printf("Both map contains key 'aaa': %v, %v\n", v1, v2)
}
在Go Playground上尝试这些示例。
英文:
No, it can't be done. Spec: Index expressions:
> An index expression on a map a of type map[K]V
used in an assignment or initialization of the special form
>
> v, ok = a[x]
> v, ok := a[x]
> var v, ok = a[x]
>
> yields an additional untyped boolean value. The value of ok
is true
if the key x
is present in the map, and false otherwise.
So you can use the special v, ok := m[k]
form only if nothing else gets assigned.
However, if you don't use the zero value of the value type of the map, you can do the check using a simple tuple-assignment; by not using the special form but 2 simple index expressions.
For example if your value type is some interface type (e.g. interface{}
), and you know you don't use the nil
value, you may do the following:
if v1, v2 := m1["aaa"], m2["aaa"]; v1 != nil && v2 != nil {
fmt.Printf("Both map contains key '%s': %v, %v\n", "aaa", v1, v2)
}
Of course with a helper function, you can do it in one step:
func idx(m1, m2 map[string]interface{}, k string) (
v1, v2 interface{}, ok1, ok2 bool) {
v1, ok1 = m1[k]
v2, ok2 = m2[k]
return
}
Using it:
if v1, v2, ok1, ok2 := idx(m1, m2, "aaa"); ok1 && ok2 {
fmt.Printf("Both map contains key '%s': %v, %v\n", "aaa", v1, v2)
}
Try the examples on the Go Playground.
答案2
得分: 0
你也可以使用可变参数(三个点)来检查多个键:
// 检查 map1 和 map2 是否为空
func checkMap(m1, m2 map[string]interface{}, keys ...string) []bool {
var isExist []bool
for _, key := range keys {
// 从 map1 检查值
_, ok := m1[key]
if ok {
isExist = append(isExist, true) // 第一次追加以避免 panic
} else {
isExist = append(isExist, false) // 第一次追加以避免 panic
}
// 从 map2 检查值
_, ok = m2[key]
if ok {
isExist[len(isExist)-1] = true
} else {
isExist[len(isExist)-1] = false
}
}
return isExist
}
然后你可以按顺序检查你的键,像这样:
result := checkMap(myMap, myMap2, "a", "b", "c", "d", "e", "f", "g")
fmt.Printf("result = %+v\n", result) // 打印结果
if result[0] {
fmt.Println("key a 在两个 map 中存在")
}
if result[1] {
fmt.Println("key b 在两个 map 中存在")
}
英文:
you could also use variadic parameter(three dots) to check multiple keys :
// check map 1 and map2 is null or not
func checkMap(m1, m2 map[string]interface{}, keys ...string) []bool {
var isExist []bool
for key := range keys {
//checking value from map 1
_, ok := m1[keys[key]]
if ok {
isExist = append(isExist, true) // append for the first time to avoid panic
} else {
isExist = append(isExist, false) // append for the first time to avoid panic
}
// checking value from map2
_, ok = m2[keys[key]]
if ok {
isExist[key] = true
} else {
isExist[key] = false
}
}
return isExist
}
And then you can check your keys in order like this :
result := checkMap(myMap, myMap2, "a", "b", "c", "d", "e", "f", "g")
fmt.Printf("result = %+v\n", result) // print the result
if result[0] {
fmt.Println("key a exist in both map")
}
if result[1] {
fmt.Println("key b exist in both map")
}
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