From 04f561c8c9a68921e08eea6358a7fb0d8c36c93d Mon Sep 17 00:00:00 2001
From: David Guijarro <guijarro.dav@gmail.com>
Date: Fri, 19 Jun 2020 17:05:43 +0200
Subject: [PATCH] feat: difference and occurrences

---
 src/difference.spec.ts  | 33 +++++++++++++++++++++++++++++++++
 src/difference.ts       | 20 ++++++++++++++++++++
 src/index.ts            |  2 ++
 src/occurrences.spec.ts | 16 ++++++++++++++++
 src/occurrences.ts      | 13 +++++++++++++
 5 files changed, 84 insertions(+)
 create mode 100644 src/difference.spec.ts
 create mode 100644 src/difference.ts
 create mode 100644 src/occurrences.spec.ts
 create mode 100644 src/occurrences.ts

diff --git a/src/difference.spec.ts b/src/difference.spec.ts
new file mode 100644
index 0000000..e6c5f6d
--- /dev/null
+++ b/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);
+  });
+});
diff --git a/src/difference.ts b/src/difference.ts
new file mode 100644
index 0000000..e11af9d
--- /dev/null
+++ b/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)));
+}
diff --git a/src/index.ts b/src/index.ts
index 73a5627..f982223 100644
--- a/src/index.ts
+++ b/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';
diff --git a/src/occurrences.spec.ts b/src/occurrences.spec.ts
new file mode 100644
index 0000000..0735590
--- /dev/null
+++ b/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);
+  });
+});
diff --git a/src/occurrences.ts b/src/occurrences.ts
new file mode 100644
index 0000000..4bc679b
--- /dev/null
+++ b/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;
+}