I have this array of dictionaries:
var dicts = [["key1": "value1", "key2": "value2"], ["key1": "value3", "key2": "value4"]]
How should I extend Array
so that I have this function:
dicts.values(of: "key1") // result: ["value1", "value3"]
I try this:
extension Array where Iterator.Element == [String: Any] { // ERROR!
func values(of key: String) -> [Any]? {
var result: [Any]?
for value in self {
let val = value as! Dictionary<String, Any>
for k in val.keys {
if k == key {
if result == nil {
result = [Any]()
}
result?.append(val[k])
break
}
}
}
return result
}
}
But I always have error marked at extension Array
declaration:
error: same-type requirement makes generic parameter 'Element' non-generic
What should I do to fix this error?
Is it right to iterate Array
with for value in self
?
Thanks
extension Sequence where Iterator.Element == [String: Any] {
func values(of key: String) -> [Any]? {
var result: [Any] = []
for value in self {
let val = value
for (k, v) in val {
if k == key {
result.append(v)
break
}
}
}
return result.isEmpty ? nil : result
}
}
var dicts: [[String: Any]] = [["key1": "value1", "key2": "value2"], ["key1": "value3", "key2": "value4"]]
dicts.values(of: "key1") // ["value1", "value3"]
or shorter version:
extension Sequence where Iterator.Element == [String: Any] {
func values(of key: String) -> [Any]? {
let result: [Any] = reduce([]) { (result, dict) -> [Any] in
var result = result
result.append(dict.filter{ $0.key == key }.map{ $0.value })
return result
}
return result.isEmpty ? nil : result
}
}
var dicts: [[String: Any]] = [["key1": "value1", "key2": "value2"], ["key1": "value3", "key2": "value4"]]
dicts.values(of: "key1")
and without reduce functionality:
extension Sequence where Iterator.Element == [String: Any] {
func values(of key: String) -> [Any]? {
var result: [Any] = []
forEach {
result.append($0.filter{ $0.key == key }.map{ $0.value })
}
return result.isEmpty ? nil : result
}
}
var dicts: [[String: Any]] = [["key1": "value1", "key2": "value2"], ["key1": "value3", "key2": "value4"]]
dicts.values(of: "key1")
Consolidated solution with compactMap
( flatMap
in Swift 3) which filters nil
values
let dicts : [[String:Any]] = [["key1": "value1", "key2": "value2"], ["key1": "value3", "key2": "value4"]]
extension Sequence where Iterator.Element == [String:Any] {
func values(of key: String) -> [Any] {
return self.compactMap {$0[key]}
}
}
dicts.values(of:"key1")
Thanks, @JMI, for your solution, which is very elegant.
I'd just like to add a little more details to your work:
extension Sequence where Iterator.Element == [String: Any] {
func values(of key: String) -> [Any]? {
var result = [Any]()
forEach {
let tmp = $0.filter{$0.key == key}.map{$0.value}
if tmp.count > 0 {
result.append(tmp[0])
}
}
return result.isEmpty ? nil : result
}
}
var dicts: [[String: Any]] = [["key1": "value1", "key2": "value2"], ["key1": "value3", "key2": "value4"]]
if let result = dicts.values(of: "key1") {
for element in result {
print("\(element) -> \(type(of: element))")
}
}
else {
print("no result")
}
Best,
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