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

paulvs · Accepted Answer · 2017-08-02 14:51:46Z

8

Try this:

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

edited Aug 2, 2017 at 14:51

answered Aug 2, 2017 at 14:47

paulvs

12.1k3 gold badges44 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Zigii Wong Over a year ago

Error: Value of type '[Item]' has no member 'id'

paulvs Over a year ago

Sorry, updated... As @vadian said though, you probably really want to use map.

Piotr Tobolski · Accepted Answer · 2017-08-02 14:54:33Z

5

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:

Reduce is giving you 2 arguments, not single tuple with 2 values
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 }

answered Aug 2, 2017 at 14:54

Piotr Tobolski

1,4069 silver badges22 bronze badges

Comments

vadian · Accepted Answer · 2017-08-02 14:50:43Z

4

You probably mean map rather than reduce

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

answered Aug 2, 2017 at 14:50

vadian

286k32 gold badges378 silver badges379 bronze badges

Collectives™ on Stack Overflow

Append property of struct to array using reduce

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related