map-filter.html

<script type="text/javascript">
  const arr = [5,1,3,2,6]
  //double - [10,2,6,4,12]
  //binary - ["101","1","11","10","110"]

  function double(x){
      return x * 2;
  }

  function triple(x){
      return x * 3;
  }

  function binary(x){
      return x .toString(2);
  }

  const output = arr.map(binary);

  console.log(output);


  //binary and and function renduring both are same.
  //not need {} when s single line function.
  // not need to write return text there

  const output1 = arr.map((x)=> x.toString(2));
  console.log(output1);



 //filter for the values like odd or even / divede by 3

 const arr1 = [5,1,3,2,6]
//filter odd values 

function isOdd(x){
  return x % 2;  
}

const output2 = arr1.filter(isOdd);
console.log(output2);

function isEven(x){
  return x % 2 === 0;  
}
const output3 = arr1.filter(isEven);
console.log(output3);

const output4 = arr1.filter((x) => x > 4);
console.log(output4);






//reduce : - is for a get a single value of array

const arr2 = [5,1,3,2,6]
//sum or max

function findSum(arr2){
  let sum = 0;
  for (let i = 0; i < arr2.length; i++){
    sum = sum + arr2[i];
  }
  return sum;
}

console.log(findSum(arr2));


// how to transform above fucntion sum and use reduce there have a 2 arguments
// acc  : - accumaliting  (store the result) like sum
// curr : - pass one by one current value like arr2[i]
// ,0 : - is a pass a default value of acc

const output5 = arr2.reduce(function(acc, curr){
  acc = acc + curr;
  return acc;
},0);

console.log(output5);


//return a max value using a reduce
const output6 = arr2.reduce(function(max, curr){
      if (curr > max) {
          max = curr;
      }
      return max;
},0 );
console.log(output6)



const users = [
    { firstName: "Ravikumar", lastName:"Patel", age: 26},
    { firstName: "Hazy", lastName:"mehuriya", age: 75},
    { firstName: "Harry", lastName:"Patel", age: 50},
    { firstName: "Harshal", lastName:"mehuriya", age: 26},
];

// List of full name by map fucntion {26: 2, 50: 1, 75: 1}

const output7 = users.map((x) => x.firstName + " " + x.lastName);
console.log(output7);

// Age count  : reduce array of object
const output8 = users.reduce(function(acc, curr){
  if(acc[curr.age]){
    acc[curr.age] = ++acc[curr.age];
  }else{
    acc[curr.age] = 1;
  }
  return acc;
}, {});
console.log(output8);



//filter userlist which is return a object default so whats you do for a get single names

const output9 = users.filter(x => x.age < 30);
console.log(output9);


// you can use map with filter for get object single value

const output10 = users.filter(x => x.age < 30).map((x) => x.firstName)
console.log(output10);

// how to get usign a reduce

const output11 = users.reduce(function(acc, curr){
    if(curr.age < 30){
      //acc.push(curr.firstName);
      acc=[...acc,curr.firstName]
    }
    return acc;
}, []);

console.log(output11);
</script>