London | 26-ITP-Sep | Chandramani Gaire | Sprint 1 | Module-Data-Group

Sprint-1/fix/median.js

@@ -6,9 +6,23 @@
 // or contains values that aren't numbers (the function is expected to throw - see the tests).
 
 function calculateMedian(list) {
+  if (!Array.isArray(list)) {
+    throw new Error("calculateMedian requires an array of numbers");
+  }
+  if (list.length === 0) {
+    throw new Error("calculateMedian requires a non-empty array");
+  }
+  for (const item of list) {
+    if (typeof item !== "number") {
+      throw new Error("calculateMedian requires an array of numbers");
+    }
+  }
   const middleIndex = Math.floor(list.length / 2);
-  const median = list.splice(middleIndex, 1)[0];
-  return median;
+  const sorted = [...list].sort((a, b) => a - b);
+  if (sorted.length % 2 === 0) {
+    return (sorted[middleIndex - 1] + sorted[middleIndex]) / 2;
+  }
+  return sorted[middleIndex];
 }
 
 module.exports = calculateMedian;

Sprint-1/implement/dedupe.js

@@ -1 +1,11 @@
-function dedupe() {}
+function dedupe(list) {
+  const result = [];
+  for (const item of list) {
+    if (!result.includes(item)) {
+      result.push(item);
+    }
+  }
+  return result;
+}
+
+module.exports = dedupe;

Sprint-1/implement/dedupe.test.js

@@ -12,17 +12,39 @@ E.g. dedupe([1, 2, 1]) returns [1, 2]
 */
 
 // Acceptance Criteria:
+describe("dedupe", () => {
+  // Given an empty array
+  // When passed to the dedupe function
+  // Then it should return an empty array
+  it("returns [] for []", () => {
+    expect(dedupe([])).toEqual([]);
+  });
 
-// Given an empty array
-// When passed to the dedupe function
-// Then it should return an empty array
-test.todo("given an empty array, it returns an empty array");
+  // Given an array with no duplicates
+  // When passed to the dedupe function
+  // Then it should return a copy of the original array
+  it("returns a copy of the array when there are no duplicates", () => {
+    const list = [1, 2, 3];
+    const result = dedupe(list);
+    expect(result).toEqual([1, 2, 3]);
+    expect(result).not.toBe(list);
+  });
+  // Given an array of strings or numbers
+  // When passed to the dedupe function
+  // Then it should return a new array with duplicates removed while preserving the
+  // first occurrence of each element from the original array.
+  it("removes duplicate numbers, keeping the first occurrence order", () => {
+    expect(dedupe([5, 1, 1, 2, 3, 2, 5, 8])).toEqual([5, 1, 2, 3, 8]);
+    expect(dedupe([1, 2, 1])).toEqual([1, 2]);
+  });
 
-// Given an array with no duplicates
-// When passed to the dedupe function
-// Then it should return a copy of the original array
+  it("treats 1 and '1' as different values", () => {
+    expect(dedupe([1, "1", 1, "1"])).toEqual([1, "1"]);
+  });
 
-// Given an array of strings or numbers
-// When passed to the dedupe function
-// Then it should return a new array with duplicates removed while preserving the 
-// first occurrence of each element from the original array.
+  it("doesn't modify the input array", () => {
+    const list = [1, 1, 2];
+    dedupe(list);
+    expect(list).toEqual([1, 1, 2]);
+  });
+});

Sprint-1/implement/describe-median.js

@@ -20,6 +20,13 @@ function calculateMedian(list) {
 }
 
 // Implement this function. See describe-median.test.js for the acceptance criteria.
-function describeMedian(list) {}
+function describeMedian(list) {
+  try {
+    const median = calculateMedian(list);
+    return `The median is ${median}`;
+  } catch (error) {
+    return `Could not calculate a median: ${error.message}`;
+  }
+}
 
 module.exports = describeMedian;

Sprint-1/implement/describe-median.test.js

@@ -16,17 +16,60 @@ message, so the caller can see what went wrong.
 const describeMedian = require("./describe-median.js");
 
 // Acceptance criteria:
+describe("describeMedian", () => {
+  // Given an array of numbers
+  // When passed to describeMedian
+  // Then it should return "The median is " followed by the median
+  // Delete this test.todo and replace it with a test.
+  it('returns "The median is 2" for [1, 2, 3]', () => {
+    expect(describeMedian([1, 2, 3])).toEqual("The median is 2");
+  });
 
-// Given an array of numbers
-// When passed to describeMedian
-// Then it should return "The median is " followed by the median
-// Delete this test.todo and replace it with a test.
-test.todo('given [1, 2, 3], returns "The median is 2"');
+  it("works for an even-length array", () => {
+    expect(describeMedian([1, 2, 3, 4])).toEqual("The median is 2.5");
+  });
 
-// Given an empty array
-// When passed to describeMedian
-// Then it should return "Could not calculate a median: calculateMedian requires a non-empty array"
+  it("works for an unsorted array", () => {
+    expect(describeMedian([3, 1, 2])).toEqual("The median is 2");
+  });
 
-// Given something that isn't an array of numbers, e.g. "banana"
-// When passed to describeMedian
-// Then it should return "Could not calculate a median: calculateMedian requires an array of numbers"
+  // Given an empty array
+  // When passed to describeMedian
+  // Then it should return "Could not calculate a median: calculateMedian requires a non-empty array"
+  it("explains the problem for an empty array", () => {
+    expect(describeMedian([])).toEqual(
+      "Could not calculate a median: calculateMedian requires a non-empty array"
+    );
+  });
+
+  // Given something that isn't an array of numbers, e.g. "banana"
+  // When passed to describeMedian
+  // Then it should return "Could not calculate a median: calculateMedian requires an array of numbers"
+  it("explains the problem for an empty array", () => {
+    expect(describeMedian([])).toEqual(
+      "Could not calculate a median: calculateMedian requires a non-empty array"
+    );
+  });
+
+  // Given something that isn't an array of numbers, explain why
+  it.each([["banana"], [42], [null], [{}]])(
+    "explains the problem when given %p instead of an array",
+    (input) => {
+      expect(describeMedian(input)).toEqual(
+        "Could not calculate a median: calculateMedian requires an array of numbers"
+      );
+    }
+  );
+
+  it("explains the problem when called with no argument", () => {
+    expect(describeMedian()).toEqual(
+      "Could not calculate a median: calculateMedian requires an array of numbers"
+    );
+  });
+
+  it("explains the problem for an array containing a non-number", () => {
+    expect(describeMedian([1, "2", 3])).toEqual(
+      "Could not calculate a median: calculateMedian requires an array of numbers"
+    );
+  });
+});

Sprint-1/implement/max.js

@@ -1,4 +1,15 @@
 function findMax(elements) {
+  if (!Array.isArray(elements)) {
+    throw new Error("findMax requires an array of numbers");
+  }
+  if (!elements.every((v) => typeof v === "number" && !Number.isNaN(v))) {
+    throw new Error("findMax requires an array of numbers");
+  }
+  let max = -Infinity;
+  for (const value of elements) {
+    if (value > max) max = value;
+  }
+  return max;
 }
 
 module.exports = findMax;

Sprint-1/implement/max.test.js

@@ -11,33 +11,65 @@ We have set things up already so that this file can see your function from the o
 */
 
 const findMax = require("./max.js");
+describe("findMax", () => {
+  // Given an empty array
+  // When passed to the max function
+  // Then it should return -Infinity
+  // Delete this test.todo and replace it with a test.
+  it("returns -Infinity for []", () => {
+    expect(findMax([])).toEqual(-Infinity);
+  });
 
-// Given an empty array
-// When passed to the max function
-// Then it should return -Infinity
-// Delete this test.todo and replace it with a test.
-test.todo("given an empty array, returns -Infinity");
+  // Given an array with one number
+  // When passed to the max function
+  // Then it should return that number
+  it("returns the only number for [1]", () => {
+    expect(findMax([1])).toEqual(1);
+  });
 
-// Given an array with one number
-// When passed to the max function
-// Then it should return that number
+  // Given an array with both positive and negative numbers
+  // When passed to the max function
+  // Then it should return the largest number overall
+  it("returns the largest of positive and negative numbers", () => {
+    expect(findMax([5, -7, 3, -5])).toEqual(5);
+  });
 
-// Given an array with both positive and negative numbers
-// When passed to the max function
-// Then it should return the largest number overall
+  // Given an array with just negative numbers
+  // When passed to the max function
+  // Then it should return the closest one to zero
+  it("returns the negative number closest to zero", () => {
+    expect(findMax([-10, -3, -20, -5])).toEqual(-3);
+  });
 
-// Given an array with just negative numbers
-// When passed to the max function
-// Then it should return the closest one to zero
+  // Given an array with decimal numbers
+  // When passed to the max function
+  // Then it should return the largest decimal number
+  it("returns the largest decimal number", () => {
+    expect(findMax([1.5, 2.25, 2.2, -0.5])).toEqual(2.25);
+  });
+  // Given an array containing a value that isn't a number
+  // When passed to the max function
+  // Then it should throw Error("findMax requires an array of numbers")
+  it("throws when the array contains a non-number", () => {
+    expect(() => findMax(["hey", 10, "hi", 60, 10])).toThrow(
+      new Error("findMax requires an array of numbers")
+    );
+  });
+  // Given something that isn't an array at all, such as "hey", 42 or no argument
+  // When passed to the max function
+  // Then it should throw Error("findMax requires an array of numbers")
+  it.each([["hey"], [42], [null], [{}]])(
+    "throws when given %p instead of an array",
+    (input) => {
+      expect(() => findMax(input)).toThrow(
+        new Error("findMax requires an array of numbers")
+      );
+    }
+  );
 
-// Given an array with decimal numbers
-// When passed to the max function
-// Then it should return the largest decimal number
-
-// Given an array containing a value that isn't a number
-// When passed to the max function
-// Then it should throw Error("findMax requires an array of numbers")
-
-// Given something that isn't an array at all, such as "hey", 42 or no argument
-// When passed to the max function
-// Then it should throw Error("findMax requires an array of numbers")
+  it("throws when called with no argument", () => {
+    expect(() => findMax()).toThrow(
+      new Error("findMax requires an array of numbers")
+    );
+  });
+});

Sprint-1/implement/mean.js

@@ -1,3 +1,21 @@
-function calculateMean(list) {}
+function calculateMean(list) {
+  if (!Array.isArray(list)) {
+    throw new Error("calculateMean requires an array of numbers");
+  }
+
+  if (list.length === 0) {
+    throw new Error("calculateMean requires a non-empty array");
+  }
+
+  if (!list.every((v) => typeof v === "number" && !Number.isNaN(v))) {
+    throw new Error("calculateMean requires an array of numbers");
+  }
+
+  let total = 0;
+  for (const value of list) {
+    total += value;
+  }
+  return total / list.length;
+}
 
 module.exports = calculateMean;