Create Objects From an Array of Key and Value like Strings

Have you ever had an array of values that you needed to convert to an object? I've run into this scenario quite a few times and wanted to write about it.

While working on the Day 4 challenge for this years Advent of Code. I came across the need to transform a large string of key and value like inputs from the challenges input data. To give a little bit of context, the Day 4 challenge provided passport input data and asked us to verify whether each passport had the required fields. The data looked like this:

ecl:#eef340 eyr:2023 hcl:#c0946f pid:244684338 iyr:2020 cid:57 byr:1969 hgt:152cm

pid:303807545 cid:213 ecl:gry hcl:#fffffd
eyr:2038 byr:1951
hgt:171cm iyr:2011

Where each piece of passport data is separated by empty space newlines (\n). The input file contained 257 entries, but I only showed a few for readability. Some of the data is formatted all in one line where others span multiple lines but ultimately each entry is separated by the empty space new line.

Formatting Input Data

If your input data is in need of transformation, to format the string into a single line. The following steps may prove useful to you. To start handling a large .txt file like the file shown above, input.txt. Start by creating a template literal by wrapping the input text in opening and closing backticks.

const input = 
`ecl:#eef340 eyr:2023 hcl:#c0946f pid:244684338 iyr:2020 cid:57 byr:1969 hgt:152cm

pid:303807545 cid:213 ecl:gry hcl:#fffffd
eyr:2038 byr:1951
hgt:171cm iyr:2011`;

Now since the input is a String data type, we have access to String.prototype.split. Therefore, it's going to be much easier to put the data from the text file into a data structure, such as an Array for manipulation.

const passportData = input.split("\n\n");

Using .split("\n\n") is the best method for transforming the input data in input.txt. This way, each passports data is stored as an array of passport strings. The multi-line entries still contain \n entities so the formatting work is not yet complete.

0: "ecl:#eef340 eyr:2023 hcl:#c0946f pid:244684338 iyr:2020 cid:57 byr:1969 hgt:152cm"
1: "pid:303807545 cid:213 ecl:gry hcl:#fffffd↵eyr:2038 byr:1951↵hgt:171cm iyr:2011"
2: "hcl:#c0946f byr:1933 eyr:2025 pid:517067213 hgt:173cm↵ecl:hzl↵iyr:2018"

Since not all the values in the input data were single line entries, they still contain a ↵ which is equivalent to the Enter key or more commonly, a newline \n. To handle this last formatting task, I thought it would be best to use Array.prototype.map since the underlying data structure is an array after using split. Then we can join together the array of strings using Array.prototype.join and leave an empty space between each string in the array.

const passportData = input.split("\n\n");
const cleanData = passportData.map(p => p.split("\n").join(" "));

Now all the formatting is done and all passport data is stored as an array of single line strings containing key/value like data.

0: "ecl:#eef340 eyr:2023 hcl:#c0946f pid:244684338 iyr:2020 cid:57 byr:1969 hgt:152cm"
1: "pid:303807545 cid:213 ecl:gry hcl:#fffffd eyr:2038 byr:1951 hgt:171cm iyr:2011"
2: "hcl:#c0946f byr:1933 eyr:2025 pid:517067213 hgt:173cm ecl:hzl iyr:2018"

Convert an array of strings to an object

I created a helper function to handle the converting. It accepts one parameter, a string, or an array of strings and splits the incoming string by a colon :. Then using a for..of statement it's quite straightforward to assign the key and value chunks to variables. The utility function looks like this:

function convertToObj(arr) {
  const obj = {};
  for (const s of arr) {
    const data = s.split(":");
    let key = data[0];
    let value = data[1].trim();
    obj[key] = value;
  }
  return obj;
}

The function could use some testing and refined logic to handle more use-cases, but to demonstrate how the utility works for an array of strings:

const converted = convertToObj(["key1: red", "key2: yellow", "key3: purple"]);

The output of console.log(converted) would be:

{
  key1: "red", 
  key2: "yellow", 
  key3: "purple"
}

In order to utilize the full potential of this helper function (specifically for the Day 4 challenge). We can use another for..of loop to invoke converToObj for each passport string in the array of strings from our formatted data.

const passportData = input.split("\n\n");
const cleanData = passportData.map(p => p.split("\n").join(" "));

for (str of cleanData) {
    const inputs = str.split(" ");
    const data = convertToDict(inputs);
    console.log(isValid(data)); // 206 valid passports :)
}

The output of data would be each passport string converted to a well defined object.

{ecl: "#eef340", eyr: "2023", hcl: "#c0946f", pid: "244684338", iyr: "2020", …}
{pid: "303807545", cid: "213", ecl: "gry", hcl: "#fffffd", eyr: "2038", …}
{hcl: "#c0946f", byr: "1933", eyr: "2025", pid: "517067213", hgt: "173cm", …}

To finish solving Day 4 part one, I wrote an isValid function to check each of the required passport fields.

function isValid(obj) {
    var byr = Object.keys(obj).includes("byr");
    var iyr = Object.keys(obj).includes("iyr");
    var eyr = Object.keys(obj).includes("eyr");
    var hcl = Object.keys(obj).includes("hcl");
    var ecl = Object.keys(obj).includes("ecl");
    var hgt = Object.keys(obj).includes("hgt");
    var pid = Object.keys(obj).includes("pid");

    return byr && iyr && eyr && hcl && ecl && hgt && pid ? obj : false;
}

Well! I may have talked about many things in this article, but hopefully the helper function for converting key and value like strings to a well defined object was clear. This article will also help you to solve part one of the Advent of Code Day 4 challenge. The source code for this can be found at tannerdolby/advent-of-code on GitHub.