Sort array of strings composed of numbers

Question

I have following array which contains strings;

let data = ["2018-1", "2018-5", "2018-11", "2018-2", "2018-10", "2018-12"];

these strings are composed of number (year and month).

Can you tell me why didn't work following function for sorting? I need sort this array from latest date to oldest. In this case from "2018-12" to "2018-1".

I am using lodash in whole project so I try use it here as well.

var result = _.sortBy(data, function(i) {
  var x = i.split("-").map(Number);
  return [x[0], x[1]];
});

can you tell me why this code doesn't work and how to fix it? Thanks.

Answer 1

I added a few more dates as proof.

let data = ["2018-1", "2018-5", "2018-11", "2018-2", "2018-10", "2018-12", "2017-5", "2019-12"];

var result = data.sort((a, b) => {
  var n1 = a.split("-");
  var n2 = b.split("-");
  n1 = parseInt(n1[0]) * 100 + parseInt(n1[1]);
  n2 = parseInt(n2[0]) * 100 + parseInt(n2[1]);
  return n1 - n2;
})

console.log(result);

Answer 2

Unfortunately, sortBy doesn't support compound keys, so your array key is converted to a string. A workaround is either to provide two separate keys:

var result = _.sortBy(data, [
    x => Number(x.split('-')[0]),
    x => Number(x.split('-')[1]),
]);

or synthesize a numeric one:

var result = _.sortBy(data, x => {
    x = x.split('-');
    return Number(x[0]) * 1000 + Number(x[1])
});

Finally, you can take a risk and try Date.parse:

var result = _.sortBy(data, Date.parse)

which looks neat, but requires some cross-browser testing.

Answer 3

You could chain the splitted deltas for year and month.

var data = ["2018-1", "2018-5", "2018-11", "2018-2", "2018-10", "2018-12", "2017-5", "2019-12"],
    result = data.sort((a, b) => {
        var aa = a.split("-"),
            bb = b.split("-");

        return aa[0] - bb[0] || aa[1] - bb[1];
    });

console.log(result);