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.

Why not use the built-in JavaScript `.sort()` method on the array? It's more flexible than the lodash sort. — Pointy, Mar 19 '18 at 18:34
the missing of leading zero for month smaller than 10 makes sorting complicated. the most easy solution would using a leading zero for month numbers and use the date string directly. — Nina Scholz, Mar 19 '18 at 18:38
The first error that I got is `Uncaught ReferenceError: _ is not defined` What do you mean with "this code doesn't work", show me the error, please — Yago Azedias, Mar 19 '18 at 18:39
the problem with this question is, you have the date in a niche sortable format, but you change it to a unsortable format for the final result. the question now is a philosophical approach to change the original given well formated back to a wrong, but needed, or just to use the well formatted date and later change the date to the wanted format. — Nina Scholz, Mar 19 '18 at 18:51
Next time, please don't tag "lodash" if you're looking for vanilla code. — georg, Mar 19 '18 at 19:18

score 2 · Accepted Answer · edited Mar 19 '18 at 18:45

2

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);

edited Mar 19 '18 at 18:45

georg

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answered Mar 19 '18 at 18:40

Sebastian Speitel

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georg · Answer 2 · 2018-03-19T18:49:33.920

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.

score 0 · Answer 3 · answered Mar 19 '18 at 19:19

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);

Sort array of strings composed of numbers

3 Answers3