Assign Integers From Dictionary Values To Characters Of A String

indices and for value in nicely gives me the loop I'm looking for however I need to go a step further and assign the values of the dictionary to the matching characters of the stri

Solution 1:

n[i] is of type Character, so that should be the key type of the dictionary instead of String. The value type should be Int:

let dict: [Character: Int] = ["a": 1, "j": 1, "s": 1, "b": 2, "k": 2, "r": 9 /* ... */]

You also have to define a "default value" which is used as score for characters not found in the dictionary, this can be done with the nil-coalescing operator ??:

let n = "lighthouse"
var nScore = 0

for i in n.indices[n.startIndex..<n.endIndex] {
    let curChar = n[i]
    let curVal = dict[curChar] ?? 0
    nScore = nScore + curVal
}

Or simpler, by enumerating the characters of the string directly:

for c in n {
    let curVal = dict[c] ?? 0
    nScore = nScore + curVal
}

Even shorter with reduce():

let n = "lighthouse"
let nScore = n.reduce(0) { (score, c) in
    score + (dict[c] ?? 0)
}

which can be written more compactly using "shorthand parameters":

let n = "lighthouse"
let nScore = n.reduce(0) { $0 + (dict[$1] ?? 0) }

If it you have full control over the possible characters which can occur in the input string, and it is guaranteed(!) the dictionary defines values for all of them then you can force-unwrap the dictionary lookup, for example

let n = "lighthouse"
let nScore = n.reduce(0) { $0 + dict[$1]! }

But this will crash at runtime if a character is not found.

---

If you define a function

func numericScore(_ str: String) -> Int {
    return str.reduce(0) { $0 + (dict[$1] ?? 0) }
}

then you can easily apply it to a single string

let nScore = numericScore("lighthouse")

or map it over an array of strings

let words = ["lighthouse", "motorcycle"]
let scores = words.map(numericScore)

or compute the total score for an array of strings (using reduce again):

let words = ["lighthouse", "motorcycle"]
let totalScore = words.reduce(0) { $0 + numericScore($1) }

// Alternatively in two steps:

let scores = words.map(numericScore)
let totalScores = scores.reduce(0, +)