Array Method Drills

Array Copying Drill 1

function firstFourItems(array) {
  return array.slice(0, 4);
}

function lastThreeItems(array) {
  return array.slice(-3);
}



/* From here down, you are not expected to 
   understand.... for now :)  
   
   
   Nothing to see here!
   
*/


// tests

function testFunctionWorks(fn, input, expected) {
  
  const result = fn(input);
  if (
    result && result.length === expected.length &&
    result.every(function(item) {
      return expected.indexOf(item) > -1;
    })) {
    console.log('SUCCESS: `' + fn.name + '` works!')
    return true;
  } 
  else {
    console.error('FAILURE: `' + fn.name + '` is not working')
    return false;
  } 
}

function runTests() {
  
  const list = ["red bull", "monster", "amp", "rockstar", "full throttle"];
  const result1 = ["red bull", "monster", "amp", "rockstar"];
  const result2 = ["amp", "rockstar", "full throttle"];
  
  const testResults = [
    testFunctionWorks(firstFourItems, list, result1),
    testFunctionWorks(lastThreeItems, list, result2),
  ];
  
  
  const numPassing = testResults.filter(function(result){ return result; }).length;
  console.log(numPassing + ' out of ' + testResults.length + ' tests passing.');
}

runTests();

Array Copying Drill 2

function minusLastItem(array) {
  return array.slice(0, (array.length -1));
}


function copyFirstHalf(array) {
  return array.slice(0, array.length/2);
}




/* From here down, you are not expected to 
   understand.... for now :)  
   
   
   Nothing to see here!
   
*/


// tests

function testFunctionWorks(fn, input, expected) {
  const result = fn(input);
  if (
    result && result.length === expected.length &&
    result.every(function(item) {
      return expected.indexOf(item) > -1;
    })) {
    console.log('SUCCESS: `' + fn.name + '` works!');
    return true;
  } else {
    console.error('FAILURE: `' + fn.name + '` is not working');
    return false;
  } 
}

function runTests() {
  
  const list = ["red bull", "monster", "amp", "rockstar", "full throttle", "kickstart"];
  const result1 = ["red bull", "monster", "amp", "rockstar", "full throttle"];
  const result2 = ["red bull", "monster", "amp"];
  
  const testResults = [
    testFunctionWorks(minusLastItem, list, result1),
    testFunctionWorks(copyFirstHalf, list, result2),
  ];
  
  
  const numPassing = testResults.filter(function(result){ return result; }).length;
  console.log(numPassing + ' out of ' + testResults.length + ' tests passing.');
}

runTests();

Array Filter Drill

function shortWords(array) {
  return array.filter(function(str){
    return str.length < 5;
  });
}






/* From here down, you are not expected to 
   understand.... for now :)  
   
   
   Nothing to see here!
   
*/


// tests

function testFunctionWorks(fn, input, expected) {
  
  const result = fn(input);
  if (
    result && result.length === expected.length &&
    result.every(function(item) {
      return expected.indexOf(item) > -1;
    })) {
    console.log('SUCCESS: `' + fn.name + '` works!')
    return true;
  } 
  else {
    console.error('FAILURE: `' + fn.name + '([' + input + '])` should be ' + expected +
      ' but was ' + fn(input))
    return false;
  } 
}

function runTests() {
  
  const input1 = ['cat', 'oblivion', 'dog', 'patriarchy', 'blue', 'house'];
  const result1 = ['cat', 'dog', 'blue'];
  const input2 = ['rainbow', 'the', 'big', 'broom'];
  const result2 = ['the', 'big'];
  
  const testResults = [
    testFunctionWorks(shortWords, input1, result1),
    testFunctionWorks(shortWords, input2, result2),
  ];
  
  
  
  const numPassing = testResults.filter(function(result){ return result; }).length;
  console.log(numPassing + ' out of ' + testResults.length + ' tests passing.');
}

runTests();

Array greatest to least drill

function greatestToLeast(array) {
  return array.sort(function(a,b){return b-a});
}






/* From here down, you are not expected to 
   understand.... for now :)  
   
   
   Nothing to see here!
   
*/


// tests

function testFunctionWorks(fn, input, expected) {
  const result = fn(input);
  if (
    result &&
    result.length === expected.length &&
    result.every(function(item, index) {
     return (index === 0 || result[index] < result[index-1]);
    }) &&
    result.every(function(item) {
      return expected.indexOf(item) > -1;
    })) {
    console.log('SUCCESS: `' + fn.name + '` works!')
    return true;
  }
  else {
    console.error('FAILURE: `' + fn.name + '([' + input + '])` should be ' + expected +
      ' but was ' + fn(input))
    return false;
  }
}

function runTests() {
  
  const input1 = [10, 3, 5, 22, 19];
  const result1 = [22, 19, 10, 5, 3];
  const input2 = [2, 4, 6, 8];
  const result2 = [8, 6, 4, 2];
  
  const testResults = [
    testFunctionWorks(greatestToLeast, input1, result1),
    testFunctionWorks(greatestToLeast, input2, result2),
  ];
  
  
  
  const numPassing = testResults.filter(function(result){ return result; }).length;
  console.log(numPassing + ' out of ' + testResults.length + ' tests passing.');
}

runTests();

Array squares with map drill

function squares(array) {
  return array.map(function(num){
  return num**2;
  }); 
}






/* From here down, you are not expected to 
   understand.... for now :)  
   
   
   Nothing to see here!
   
*/


// tests

function testFunctionWorks(fn, input, expected) {
  
  const result = fn(input);
  if (
    result && result.length === expected.length &&
    result.every(function(item) {
      return expected.indexOf(item) > -1;
    })) {
    console.log('SUCCESS: `' + fn.name + '` works!')
    return true;
  } 
  else {
    console.error('FAILURE: `' + fn.name + '([' + input + '])` should be ' + expected +
      ' but was ' + fn(input))
    return false;
  } 
}

function runTests() {
  
  const input1 = [1, 2, 3, 4, 5];
  const result1 = [1, 4, 9, 16, 25];
  const input2 = [2, 4, 6, 8];
  const result2 = [4, 16, 36, 64];
  
  const testResults = [
    testFunctionWorks(squares, input1, result1),
    testFunctionWorks(squares, input2, result2),
  ];
  
  
  
  const numPassing = testResults.filter(function(result){ return result; }).length;
  console.log(numPassing + ' out of ' + testResults.length + ' tests passing.');
}

runTests();

Find Divisible by 5 Drill

function divisibleBy5(array) {
  return array.find( function(num) {
    return num % 5 === 0;
  });
}

/* From here down, you are not expected to 
   understand.... for now :)  
   
   
   Nothing to see here!
   
*/


// tests

function testFunctionWorks(fn, input, expected) {
  
  if (fn(input) === expected) {
    console.log('SUCCESS: `' + fn.name + '` works on `[' + input + ']`');
    return true;
  }
  else {
    console.error(
      'FAILURE: `' + fn.name + '([' + input + '])` should be ' + expected +
      ' but was ' + fn(input)
    );
    return false;
  } 
}

function runTests() {
  
  const input1 = [13, 22, 4, 47, 15, 35, 82];
  const result1 = 15;
  const input2 = [25, 20, 15, 10, 5];
  const result2 = 25;
  
  const testResults = [
    testFunctionWorks(divisibleBy5, input1, result1),
    testFunctionWorks(divisibleBy5, input2, result2),
  ];
  
  
  
  const numPassing = testResults.filter(function(result){ return result; }).length;
  console.log(numPassing + ' out of ' + testResults.length + ' tests passing.');
}

runTests();