Group elements with the same property value from an array [duplicate] - ios

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How to group by the elements of an array in Swift
(16 answers)
Closed 6 years ago.
I have an array [modelA,modelB,modelC,modelD,modelE], each element in the array is an instance of a Struct. The Struct has a property "name". for example...
modelA.name = "abc"
modelB.name = "efg"
modelC.name = "hij"
modelD.name = "abc"
modelE.name = "efg"
How can I group elements with the same property value into a new array? i.e. put modelA and modelD into a new array,and put modelB and modelE into another array.
Assume the original array is large.

Answer 1

You can achieve this by using filter(_:):
Returns an array containing, in order, the elements of the sequence
that satisfy the given predicate.
For example, consider that the structure looks like:
struct Model {
var name: String?
}
And you have an array of models:
let allModelsArray = [Model(name: "abc"), Model(name: "efg"), Model(name: "hij"), Model(name: "abc"), Model(name: "efg"), Model(name: "efg"), Model(name: "hij")]
So, you can get your arrays by doing (assuming that you want to filter based on the value of the name):
let abcModelsArray = allModelsArray.filter { $0.name == "abc" }
// [Model(name: Optional("abc")), Model(name: Optional("abc"))]
let hijModelsArray = allModelsArray.filter { $0.name == "hij" }
// [Model(name: Optional("hij")), Model(name: Optional("hij"))]
ALSO:
You mentioned that:
how can I put element which has the same property value into a new
array, such as put modelA and modelD into a new array, and put modelB
and modelE into a new array, if array is large.
Somehow, you might want to use the lazy version of the collection.
Hope this helped.

Answer 2

I have not performance tested this
struct Model {
var type : String
var name : String
}
var modelA = Model(type: "A", name: "abc")
var modelB = Model(type: "B", name: "efg")
var modelC = Model(type: "C", name: "abc")
var modelD = Model(type: "D", name: "efg")
let models = [modelA,modelB,modelC,modelD]
let names = Set(models.map({return $0.name}))
var groupedModels : [String:[Model]] = [:]
for var name in names {
let elements = models.filter({$0.name == name})
groupedModels[name] = elements
}

Answer 3

.reduce solution:
let a = [modelA, modelB, modelC, modelD, modelE]
let arr = a.reduce([:]) { (result, currentModel) -> [String: [Model]] in
var mutableDic = result
if ((mutableDic[currentModel.name]) != nil) {
mutableDic[currentModel.name]?.append(currentModel)
} else {
mutableDic[currentModel.name] = [currentModel]
}
return mutableDic
}
It will return the same dictionary as #Grimxn response. or got from this for loop
var mutableDic = [String : [Model]]()
for aModel in a {
if ((mutableDic[aModel.name]) != nil) {
mutableDic[aModel.name]?.append(aModel)
} else {
mutableDic[aModel.name] = [aModel]
}
}
The key is to use a Dictionary to track for Model that need to be put in the same array, by comparing to it's .name.