Append property of struct to array using reduce

Question

I have an array of Items

struct Item {
    var id: String
}

How can I append all the ids to an array using reduce function?

What I try:

self.items.reduce([String](), { $0.0.append($0.1.id)})

But compiler shows an error:

Contextual closure type '(_, [Item]) -> _' expects 2 arguments, but 1 was used in closure body

Answer 1

Try this:

items.reduce([String](), { res, item in
    var arr = res
    arr.append(item.id)
    return arr
})

Answer 2

If you want to do it with reduce, here is a snippet for Swift 3 and 4:

struct Item {
    var id: String
}

var items = [Item(id: "text1"), Item(id: "text2")]
let reduceResult = items.reduce([String](), { $0 + [$1.id] } )
reduceResult // ["text1", "text2"]

There were 2 issues:

1. Reduce is giving you 2 arguments, not single tuple with 2 values
2. You can't edit argument that is passed to you in the block, you have to return new object

But in this case the best solution is to use map:

let reduceResult = items.map { $0.id }

Answer 3

You probably mean map rather than reduce

let ids = items.map{ $0.id }