Mastering the art of utilizing array.map efficiently

Question

Mastering the art of utilizing array.map efficiently

I'm puzzled as to why my array.map function is returning undefined, but my for loop is returning the result. When I console log map, it displays:

Tom Dick Harry

and when I console log the for loop, it shows:

['Tom', 'Dick', 'Harry']

I'm unsure if this issue is related to showing undefined.

var friends = ["Tom", "Dick", "Harry"];
var secondLevelFriends = ["Anne", "Harry", "Quinton"];
var allUsers = ["Tom", "Dick", "Harry", "Anne", "Quinton", "Katie", "Mary"];

function findPotentialFriends(existingFriends) {
  return function(x) {
    // existingFriends.map(function(elem) {
    //   if(elem === x) return false;
    //   else return true;
    // })
    for(var i = 0; i < existingFriends.length; i++) {
      if(existingFriends[i] === x) return false;
      else return true;
    }
  }
}

var isNotAFriend = findPotentialFriends( friends );
isNotAFriend(allUsers[0]); // false

javascript arrays

Answer 1

Answer №1

To begin with, your for loop contains some logical errors and should be adjusted as follows:

var foundFriend = false;
for(var i = 0; i < existingFriends.length; i++) {
  if (existingFriends[i] === x)
  {
    foundFriend = true;
    break;
  }
}
return !foundFriend;

The reason why the variable isNotAFriend results in undefined is due to the omission of a return statement. Additionally, the Arrays.map method simply takes each element of the array, passes it into the function, and creates a new array based on the return value of the function. If you are looking for a different functionality, consider using Array.some, you can find more information in the documentation. Here's an example:

var friends = ["Tom", "Dick", "Harry"];
var secondLevelFriends = ["Anne", "Harry", "Quinton"];
var allUsers = ["Tom", "Dick", "Harry", "Anne", "Quinton", "Katie", "Mary"];

function findPotentialFriends(existingFriends) {
  return function(x) {
    return !existingFriends.some(function(elem) {
      return elem === x;
    });
  }
}

var isNotAFriend = findPotentialFriends( friends );
console.log(isNotAFriend(allUsers[0]));

Answer 2

To begin with, your for loop contains some logical errors and should be adjusted as follows:

var foundFriend = false;
for(var i = 0; i < existingFriends.length; i++) {
  if (existingFriends[i] === x)
  {
    foundFriend = true;
    break;
  }
}
return !foundFriend;

The reason why the variable isNotAFriend results in undefined is due to the omission of a return statement. Additionally, the Arrays.map method simply takes each element of the array, passes it into the function, and creates a new array based on the return value of the function. If you are looking for a different functionality, consider using Array.some, you can find more information in the documentation. Here's an example:

var friends = ["Tom", "Dick", "Harry"];
var secondLevelFriends = ["Anne", "Harry", "Quinton"];
var allUsers = ["Tom", "Dick", "Harry", "Anne", "Quinton", "Katie", "Mary"];

function findPotentialFriends(existingFriends) {
  return function(x) {
    return !existingFriends.some(function(elem) {
      return elem === x;
    });
  }
}

var isNotAFriend = findPotentialFriends( friends );
console.log(isNotAFriend(allUsers[0]));

Answer 3

Answer №2

The issue with the code provided is that the return statements within the callback only return to the map() function itself, and not to the original caller. The map() function then collects all these return values into an array without performing any further actions with the result of existingfriends.map().

In JavaScript, there is a predefined method for searching an array for a specific element called Array.prototype.indexOf(), which returns -1 if no match is found.

You can simplify the code by using the following approach:

var friends = ["Tom", "Dick", "Harry"];
var secondLevelFriends = ["Anne", "Harry", "Quinton"];
var allUsers = ["Tom", "Dick", "Harry", "Anne", "Quinton", "Katie", "Mary"];

function findPotentialFriends(existingFriends) {
  return function(x) {
   return existingFriends.indexOf(x) == -1;   
  }
}

var isNotAFriend = findPotentialFriends(friends);
console.log(isNotAFriend(allUsers[0])); // false

Answer 4

The issue with the code provided is that the return statements within the callback only return to the map() function itself, and not to the original caller. The map() function then collects all these return values into an array without performing any further actions with the result of existingfriends.map().

In JavaScript, there is a predefined method for searching an array for a specific element called Array.prototype.indexOf(), which returns -1 if no match is found.

You can simplify the code by using the following approach:

var friends = ["Tom", "Dick", "Harry"];
var secondLevelFriends = ["Anne", "Harry", "Quinton"];
var allUsers = ["Tom", "Dick", "Harry", "Anne", "Quinton", "Katie", "Mary"];

function findPotentialFriends(existingFriends) {
  return function(x) {
   return existingFriends.indexOf(x) == -1;   
  }
}

var isNotAFriend = findPotentialFriends(friends);
console.log(isNotAFriend(allUsers[0])); // false

Answer 5

Answer №3

To implement the new functionality in the map() function, make sure to include the return statement within it. This function is nested inside another function and must also be returned accordingly.

var friends = ["Tom", "Dick", "Harry"];
var secondLevelFriends = ["Anne", "Harry", "Quinton"];
var allUsers = ["Tom", "Dick", "Harry", "Anne", "Quinton", "Katie", "Mary"];

function findPotentialFriends(existingFriends) {
  return function(x) {
   return existingFriends.map(function(elem) {
  if(elem === x) return false;
     else return true;
    })
   // for(var i = 0; i < existingFriends.length; i++) {
    //  if(existingFriends[i] === x) return false;
     // else return true;
    //}
  }
}

var isNotAFriend = findPotentialFriends(friends);
console.log(isNotAFriend(allUsers[0])); // false

Answer 6

To implement the new functionality in the map() function, make sure to include the return statement within it. This function is nested inside another function and must also be returned accordingly.

var friends = ["Tom", "Dick", "Harry"];
var secondLevelFriends = ["Anne", "Harry", "Quinton"];
var allUsers = ["Tom", "Dick", "Harry", "Anne", "Quinton", "Katie", "Mary"];

function findPotentialFriends(existingFriends) {
  return function(x) {
   return existingFriends.map(function(elem) {
  if(elem === x) return false;
     else return true;
    })
   // for(var i = 0; i < existingFriends.length; i++) {
    //  if(existingFriends[i] === x) return false;
     // else return true;
    //}
  }
}

var isNotAFriend = findPotentialFriends(friends);
console.log(isNotAFriend(allUsers[0])); // false

Mastering the art of utilizing array.map efficiently

Answer №1

Answer №2

Answer №3

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