feat: difference and occurrences

src/difference.spec.ts

@@ -0,0 +1,33 @@
+import { difference } from './difference';
+
+describe('difference', () => {
+  it('should return a new array the difference between two arrays', () => {
+    const a = ['a', 'b', 'c', 'd'];
+    const b = ['b', 'c'];
+    const e = ['a', 'd'];
+
+    expect(difference(a, b)).toEqual(e);
+  });
+
+  it('should support second array being bigger than first', () => {
+    const a = ['b', 'c'];
+    const b = ['a', 'b', 'c', 'd'];
+    const e = ['a', 'd'];
+
+    expect(difference(a, b)).toEqual(e);
+  });
+
+  it('should return empty array if both input arrays are equal', () => {
+    const a = ['a', 'b', 'c', 'd'];
+    const b = [...a];
+    expect(difference(a, b)).toEqual([]);
+  });
+
+  it('should support arrays of objects', () => {
+    const a = [{ first: 'first', second: 'second' }, { third: 'third' }];
+    const b = [{ third: 'third' }];
+    const e = [{ first: 'first', second: 'second' }];
+
+    expect(difference(a, b)).toEqual(e);
+  });
+});

src/difference.ts

@@ -0,0 +1,20 @@
+import { isEqual } from './is-equal';
+
+/**
+ * Takes two arrays and returns the difference between them as a new array.
+ * In this case, "difference" is to be understood as the elements of one array not present in the other.
+ *
+ * @param first First array.
+ * @param second Second array.
+ */
+
+export function difference<T>(first: T[], second: T[]): T[] {
+  if (isEqual(first, second)) {
+    return [];
+  }
+
+  if (second.length > first.length) {
+    [second, first] = [first, second];
+  }
+  return first.filter(f => !second.some(s => isEqual(f, s)));
+}

src/index.ts

@@ -4,3 +4,5 @@ export * from './random';
 export * from './sample';
 export * from './shuffle';
 export * from './omit';
+export * from './occurrences';
+export * from './difference';

src/occurrences.spec.ts

@@ -0,0 +1,16 @@
+import { occurrences } from './occurrences';
+
+describe('occurrences', () => {
+  it('should count one character occurrences in a string', () => {
+    expect(occurrences('mississippi', 'i')).toBe(4);
+  });
+
+  it('should count substring occurrences in a string', () => {
+    expect(occurrences('mississippi', 'ssi')).toBe(2);
+  });
+
+  it('should return zero if any argument is an empty string', () => {
+    expect(occurrences('', 'e')).toBe(0);
+    expect(occurrences('mississippi', '')).toBe(0);
+  });
+});

src/occurrences.ts

@@ -0,0 +1,13 @@
+/**
+ * Returns the number of times that a substring `search` appears in a string `input`.
+ *
+ * @param input The string to search in.
+ * @param search The substring to be searched.
+ */
+
+export function occurrences(input: string, search: string): number {
+  if (input === '' || search === '') {
+    return 0;
+  }
+  return (input.match(new RegExp(search, 'g')) || []).length;
+}