Readable List from Array • Debjit's Digital Home

I recently came across a problem of rendering an array of strings as a human readable string in the format: “A, B and C”. It didn’t seem too difficult at first but I decided to do this in a more functional way, without using a loop. Additionaly it needed to work with arrays of single element and even an empty array.

The cases are:

[]              -> ""
[""]            -> ""
["A"]           -> "A"
["A", "B"]      -> "A and B"
["A", "B", "C"] -> "A, B and C"

… and so on

First let’s look at a naive solution with a loop. This can be improved and optimized, but I was not interested in such a solution, so I din’t explore it further.

function getReadableString(a) {
    var l = a.length,
        str = "";

    for (var i = 0; i < l; i += 1) {

        if (l < 2) {
            str = a[i] || "";
            continue;
        }

        if (i === l - 1 && l > 1) {
            str += "and " + a[i];
        } else if (i === 0 && l === 2) {
            str += a[i] + " ";
        } else {
            str += a[i] + ", ";
        }
    }

    return str;
}

That is such mess, lets change that:

function getReadableString(a) {
    var l = a.length,
        str = "";

    switch(l) {
    case 0:
        str = "";
        break;
    case 1:
        str = a[0]
        break;
    case 2:
        str = a.join(" and ");
        break;
    default:
        str = a.slice(0, -1).join(", ") + " and " + [a.pop()]
    };

    return str;
}

Now, that looks organized. Still, if somehow we can include the cases for array length being 0, 1 or 2 in the default logic, we would have a nicer solution.

function getReadableString(a) {
    return [
            a

            /* Get all the elements except the last one.
             * If there is just one element, get that
             */
            .slice(0, a.length - 1 || 1)

            /* Create a comma separated string from these elements */
            .join(", ")
        ]
        /* Process the last element (if there is one) and concat it
         * with the processed first part.
         */
        .concat(
            a

            /* Create a copy */
            .slice()

            /* Take the last element, if there is one */
            .splice(-1, Number(a.length > 1))
        )

        /* Join the two processed parts */
        .join(" and ");
}

Is there a better solution? I am still looking.

Update: Ok, so one of my friends suggested a solution, by joining the array and replacing the last comma as with ‘and’. I must admit that the solution has a beauty of its own.

function getReadableString(a) {
    return a.join(', ').replace(/(.*),\s([^,]*)$/,'$1 and $2');
}

I am not sure if the regex used is the best possible, but it works. The disadvantage of this solution is that it cannot be extended to create strings such as ‘A, B, C and 4 others’, while the previous solution can be,

function getReadableString(a) {
    var l = a.length;

    return ([a
            .slice(0, Number(l > 2) + 1)
            .join(", ")
        ]
        .concat(l < 4 ? a.slice().splice(-1, Number(l > 1)) : l - 2 + " others")
        .join(" and ") || "None");
}

Another disadvantage, it is not as much fun as the previous one ☺.