Swift: Merge Array of dictionaries with duplicate key but unique values

Question

I have a array of dictionaries which contains same key but different values. I want to merge these dictionaries and add all the values of same keys just like below:

var arrayofDict = [["2019":"A"],["2019":"B"],["2019":"C"],["2018":"A"],["2018":"c"],["2017":"A"],["2017":"B"],["2017":"C"],["2016":"A"],["2015":"A"],["2015":"B"]]

expected result as an Array like:

   var newDict = [["2019":["A","B","C"]],["2018":["A","C"]],["2017":["A","B","C"]],["2016":["A"]],["2015":["A","B"]]]

"I have a array of dictionaries which contains same key but different values." I'm curious: Where did you get it from? Do you have control over that data? — Alexander
– Alexander, Commented Jan 31, 2020 at 16:35

vacawama · Accepted Answer · 2020-01-31 16:48:39Z

4

This shows how to build a single dictionary. Your "expected result" is an array. Is this what you really expected or did you want an array?

You can iterate the dictionary items and build up the dictionary entries:

var arrayofDict = [["2019":"A"],["2019":"B"],["2019":"C"],["2018":"A"],["2018":"c"],["2017":"A"],["2017":"B"],["2017":"C"],["2016":"A"],["2015":"A"],["2015":"B"]]

var result = [String : [String]]()
for dict in arrayofDict {
    for (key, value) in dict {
        result[key, default: []].append(value)
    }
}

print(result)

["2016": ["A"], "2018": ["A", "c"], "2015": ["A", "B"], "2019": ["A", "B", "C"], "2017": ["A", "B", "C"]]

Or, if you want an array:

let result2 = result.map { [$0.key: $0.value] }
print(result2)

[["2015": ["A", "B"]], ["2016": ["A"]], ["2019": ["A", "B", "C"]], ["2018": ["A", "c"]], ["2017": ["A", "B", "C"]]]

edited Jan 31, 2020 at 16:48

answered Jan 31, 2020 at 16:40

vacawama

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2 Comments

user1256276 Over a year ago

How to sort this in descending order of the year? and also sort values too? @vacawama

vacawama Over a year ago

let result2 = result.map { [$0.key: $0.value.sorted()] }; let result3 = result2.sorted(by: { $0.first!.key > $1.first!.key } )

user3441734 · Accepted Answer · 2020-02-01 12:12:56Z

0

as @vacawama in more functional way

let result = arrayofDict.reduce(into: [String:[String]]()) { (acc, d) in
    for key in d.keys {
        // don't worry to force unwrap d[key], if key exist, the value is not nil
        acc[key, default: []].append(d[key]!)
    }
}

answered Feb 1, 2020 at 12:12

user3441734

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