[swift-evolution] map-like operation that returns a dictionary

[Ian Ynda-Hummel]

I think this probably wants to be a `reduce`. Given the above example:

    ["John", "Mike", "Amy", "Kavin"].enumerate().reduce([Int: String]()) {
(var dictionary, data) in
        dictionary[data.index] = data.element
        return dictionary
    }

Which means you create an immutable dictionary with `let`. This could
probably look nicer, but I think it illustrates the idea, at least.

-Ian

On Sun, Jan 10, 2016 at 2:46 PM Craig Cruden via swift-evolution <
swift-evolution at swift.org> wrote:

> There is no equivalent to something like
>
> array.zipWithIndex.toMap (or in this case array.zipWithIndex.toDictionary
> // where zipWithIndex creates tuples with the index - a specialized case of
> zip for Arrays with indexes.
>
>
>
> On 2016-01-11, at 2:41:59, Ross O'Brien via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Or an enumeration followed by a forEach.
> ["John", "Mike", "Amy", Kavin"].enumerate().forEach {
>     dic[$0] = $1
> }
> That said, it requires creating a dictionary var first, not a let. If
> there was an initialiser for Dictionary which took an Array or
> EnumerateSequence, that might be useful. I'm not sure how I'd attempt to
> write such an initialiser though.
>
>
> On Sun, Jan 10, 2016 at 7:08 PM, Donnacha Oisín Kidney <
> swift-evolution at swift.org> wrote:
>
>> I think that use of map is generally discouraged. forEach would probably
>> be more explicit, or a for-loop.
>>
>> On 10 Jan 2016, at 18:58, 肇鑫 via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> You can use dictionary in a map. You just ignore the return value of the
>> map.
>>
>> var dic = [Int:String]()
>> var index = 0
>>
>> ["John", "Mike", "Amy", "Kavin"].map {
>>     dic.updateValue($0, forKey: index)
>>     index += 1
>> }
>>
>> print(dic) // [2: "Amy", 0: "John", 1: "Mike", 3: "Kavin"]
>>
>> zhaoxin
>>
>> On Mon, Jan 11, 2016 at 1:50 AM, Kenny Leung via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>> Hi All.
>>>
>>> I find that instead of using map() on arrays, I more often use an
>>> operation that returns a dictionary from an array. A common case is
>>> fetching an array of data, then creating a local cache of it indexed by ID.
>>>
>>> Is there a name for this operation? Is this something that others would
>>> like to see added to the standard library?
>>>
>>> -Kenny
>>>
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>
>>
>>
>>
>> --
>>
>> Owen Zhao
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>>
>>
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