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feat(orderBy): Stable sort the input array #12408

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feat(orderBy): Stable sort the input array #12408

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4 changes: 4 additions & 0 deletions src/ng/filter/orderBy.js
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,10 @@ function orderByFilter($parse) {
if (sortPredicate.length === 0) { sortPredicate = ['+']; }

var predicates = processPredicates(sortPredicate, reverseOrder);
// Add a predicate at the end that evaluates to the element index. This makes the
// sort stable as it works as a tie-breaker when all the input predicates cannot
// distinguish between two elements.
predicates.push({ get: function() { return {}; }, descending: reverseOrder ? -1 : 1});
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I think we should leave a comment explaining this, it won't be very nice to have to look up this issue in the blame for this function to figure out what this means once it stops being clear, otherwise this looks maybe a bit brittle

Just a quick header comment with an overview explaining how the predicate works, imho


// The next three lines are a version of a Swartzian Transform idiom from Perl
// (sometimes called the Decorate-Sort-Undecorate idiom)
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29 changes: 29 additions & 0 deletions test/ng/filter/orderBySpec.js
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Expand Up @@ -194,6 +194,35 @@ describe('Filter: orderBy', function() {
it('should sort mixed array of objects and values in a stable way', function() {
expect(orderBy([{foo: 2}, {foo: {}}, {foo: 3}, {foo: 4}], 'foo')).toEqualData([{foo: 2}, {foo: 3}, {foo: 4}, {foo: {}}]);
});


it('should perform a stable sort', function() {
expect(orderBy([
{foo: 2, bar: 1}, {foo: 1, bar: 2}, {foo: 2, bar: 3},
{foo: 2, bar: 4}, {foo: 1, bar: 5}, {foo: 2, bar: 6},
{foo: 2, bar: 7}, {foo: 1, bar: 8}, {foo: 2, bar: 9},
{foo: 1, bar: 10}, {foo: 2, bar: 11}, {foo: 1, bar: 12}
], 'foo'))
.toEqualData([
{foo: 1, bar: 2}, {foo: 1, bar: 5}, {foo: 1, bar: 8},
{foo: 1, bar: 10}, {foo: 1, bar: 12}, {foo: 2, bar: 1},
{foo: 2, bar: 3}, {foo: 2, bar: 4}, {foo: 2, bar: 6},
{foo: 2, bar: 7}, {foo: 2, bar: 9}, {foo: 2, bar: 11}
]);

expect(orderBy([
{foo: 2, bar: 1}, {foo: 1, bar: 2}, {foo: 2, bar: 3},
{foo: 2, bar: 4}, {foo: 1, bar: 5}, {foo: 2, bar: 6},
{foo: 2, bar: 7}, {foo: 1, bar: 8}, {foo: 2, bar: 9},
{foo: 1, bar: 10}, {foo: 2, bar: 11}, {foo: 1, bar: 12}
], 'foo', true))
.toEqualData([
{foo: 2, bar: 11}, {foo: 2, bar: 9}, {foo: 2, bar: 7},
{foo: 2, bar: 6}, {foo: 2, bar: 4}, {foo: 2, bar: 3},
{foo: 2, bar: 1}, {foo: 1, bar: 12}, {foo: 1, bar: 10},
{foo: 1, bar: 8}, {foo: 1, bar: 5}, {foo: 1, bar: 2}
]);
});
});


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