1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
import { assertEquals } from "../assert/mod.ts";import { distinctBy } from "./distinct_by.ts";
function distinctByTest<I>(  array: Array<I>,  selector: (element: I) => unknown,  expected: Array<I>,  message?: string,) {  const actual = distinctBy(array, selector);  assertEquals(actual, expected, message);}
Deno.test({  name: "distinctBy() handles identities on empty array",  fn() {    distinctByTest(      [],      () => {},      [],    );  },});
Deno.test({  name: "distinctBy() gets head on noop selector",  fn() {    distinctByTest(      [25, "asdf", true],      () => {},      [25],    );  },});
Deno.test({  name: "distinctBy() removes duplicates and preserves order on identity",  fn() {    distinctByTest(      [true, "asdf", 4, "asdf", true],      (it) => it,      [true, "asdf", 4],    );    distinctByTest(      [null, undefined, null, "foo", undefined],      (it) => it,      [null, undefined, "foo"],    );  },});
Deno.test({  name: "distinctBy() does not check for deep equality on identity",  fn() {    const objects = [{ foo: "bar" }, { foo: "bar" }];    distinctByTest(      objects,      (it) => it,      objects,    );
    const arrays = [[], []];    distinctByTest(      arrays,      (it) => it,      arrays,    );
    const nans = [NaN, NaN];    distinctByTest(      nans,      (it) => it,      [nans[0]],    );
    const noops = [() => {}, () => {}];    distinctByTest(      noops,      (it) => it,      noops,    );
    const sets = [new Set(), new Set()];    distinctByTest(      sets,      (it) => it,      sets,    );  },});
Deno.test({  name: "distinctBy() handles distincts by selected value and preserves order",  fn() {    const kim = { name: "Kim", age: 22 };    const arthur = { name: "Arthur", age: 22 };    const anna = { name: "Anna", age: 48 };    const karl = { name: "Karl", age: 48 };    const people = [kim, arthur, anna, karl];
    distinctByTest(      people,      (it) => it.name.charAt(0),      [kim, arthur],    );    distinctByTest(      people,      (it) => it.age,      [kim, anna],    );    distinctByTest(      people,      (it) => it.name.length,      [kim, arthur, anna],    );  },});