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JavaScript JavaScript Array Iteration Methods Array Manipulation Practice reduce()

Anik Devaughn
Anik Devaughn
7,751 Points
Posted by Anik Devaughn
Anik Devaughn
7,751 Points

Challenge Task 1 of 1 phoneNumbers is array of 10 digit phone numbers, where the first three digits, in parentheses, ar

Hi, I have tried in many ways to solve this Challenge but no luck so far. And now I am Frustrated and need some help... Please can anyone tell me what mistake I am making here. Thanks in Advance !!! My Code: const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"]; let numberOf503;

// numberOf503 should be: 3 // Write your code below numberOf503 = phoneNumbers.reduce((count, name) => { if(name[0] === "503") { return count + 1; } return count; }, 0 );

//console.log(numberOf503);

app.js 
const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"];
let numberOf503;

// numberOf503 should be: 3
// Write your code below
numberOf503 = phoneNumbers.reduce((count, name) => {
  if(name[0] === "503") {
    return count + 1;
  }
   return count;
}, 0 );

//console.log(numberOf503);

9 Answers

Valeshan Naidoo
Valeshan Naidoo
27,008 Points
Valeshan Naidoo
Valeshan Naidoo
27,008 Points

So in this instance, you need think about whether name[0] is really going to give you "503", since the strings start with "(", and name[0] will search for the first character only. The better condition would be to use the startsWith method, with this, you can check for the beginning of any string and the value can be however long.

numberOf503 = phoneNumbers.reduce((numbers, number)=> {
                                                 if (number.startsWith('(503)')) {
                                                  return numbers+1} return numbers}, 0);

I could just even use startsWith('(5') if I wanted to.

Valeshan Naidoo
Valeshan Naidoo
27,008 Points
Valeshan Naidoo
Valeshan Naidoo
27,008 Points

You could also use your method, but with a little modification

const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"];
let numberOf503;

// numberOf503 should be: 3
// Write your code below
numberOf503 = phoneNumbers.reduce((count, name) => {
  if(name[1] === "5") {
    return count + 1;
  }
   return count;
}, 0 );
Athena Ozanich
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Athena Ozanich
Front End Web Development Techdegree Graduate 29,847 Points
Athena Ozanich
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Athena Ozanich
Front End Web Development Techdegree Graduate 29,847 Points

For that matter one could also use a conditional ternary to complete this task!

numberOf503 = phoneNumbers.reduce((numOfMatches, phnNum) => {
  return ( phnNum.startsWith("(503)")?numOfMatches+1:numOfMatches) 
}, 0);

NOTE: I used the .startsWith() method to check that the string begins with the desired search, I also included the parenthesis for the area code for good measure to help, ensure to sneaky little bugs get in >,<

Bartlomiej Zabielski
PLUS
Bartlomiej Zabielski
Courses Plus Student 10,363 Points
Bartlomiej Zabielski
Bartlomiej Zabielski
Courses Plus Student 10,363 Points 
numberOf503 = phoneNumbers.reduce((acc, cur) => {
  if (cur.substring(1, 4) === "503") {
    return acc + 1;
  } else {
    return acc;
  }
}, 0);

console.log(numberOf503);
jonathanj
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jonathanj
UX Design Techdegree Student 9,378 Points
jonathanj
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jonathanj
UX Design Techdegree Student 9,378 Points

This is correct in that I used reduce to cycle through entire array. Having used an array method --> REDUCE <--- and having yielded the correct result, which in this case is 3 the tester should recognize my answer as correct should it not?

const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"];
let numberOf503;

// numberOf503 should be: 3
// Write your code below

phoneNumbers.reduce((count,areaCode)=>{
  if(areaCode.includes('(503) ')){
    count+=1
  }numberOf503 = count;
  return numberOf503;
},0);

Thanks in advance for any assistance/clarity members of the community provide. Blessings, Jonathan

jonathanj
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jonathanj
UX Design Techdegree Student 9,378 Points

I ended up going with this solution to satisfy the platform's tester...

numberOf503 = phoneNumbers.reduce((count,areaCode)=>{
  if(areaCode.includes('(503) ')){
    count+=1;
  }
  return count;
},0);```

...but I would still like to discuss what I initially crafted just above this post as well if possible. 
Thanks much everyone.
Blessings, Jonathan
Ivo Culic
Ivo Culic
389 Points
Ivo Culic
Ivo Culic
389 Points

Or one liner:

numberOf503 = phoneNumbers.reduce((acc, number) => (number.substring(1, 4) === "503") ?  acc + 1 : acc, 0);
Anik Devaughn
Anik Devaughn
7,751 Points
Anik Devaughn
Anik Devaughn
7,751 Points

Thanks alot ! It works

joakim edwardh
joakim edwardh
1,720 Points
joakim edwardh
joakim edwardh
1,720 Points

I understand everything exept the 0 at the end. When i did the same code without the last 0 only the whole first number ("(503) 123-4567") was returned. Can someone please explain how the last 0 works?

Valeshan Naidoo
Valeshan Naidoo
27,008 Points
Valeshan Naidoo
Valeshan Naidoo
27,008 Points

The last 0 is the base number in which the reduce function is able to accumulate from. For example, if we were totaling the cost of a list of items, the base can be set to 0 and then it adds from there. We could also have the total to whatever number we like. If the base number is omitted, the reduce function then starts at the value of the first item. In the case of the telephone numbers, we are calculating a total of the numbers beginning with a particular prefix, so we would like the base to be 0.

Sebastian Nadeau
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Sebastian Nadeau
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Sebastian Nadeau
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Sebastian Nadeau
Front End Web Development Techdegree Student 26,545 Points

This is what I put as my answer. Why do we include + 1 in the if statement and 0 at the end of the function? Just to clarify, is the if statement after the arrow function part of a callback function? I would really appreciate someone pointing out the different parts of this code, as it gets a little confusing.

const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"];
let numberOf503;

// numberOf503 should be: 3
// Write your code below

numberOf503 = phoneNumbers.reduce((numbers, number) => {
    if (number.startsWith('(503)')) {
      return numbers + 1;
    } return numbers;
  }, 
0);
David Shulkin
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David Shulkin
Front End Web Development Techdegree Student 10,254 Points
David Shulkin
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David Shulkin
Front End Web Development Techdegree Student 10,254 Points

Hi all! You can solve this using the slice() method 

const phoneNumbers = ["(503) 123-4567", "(646) 123-4567", "(503) 987-6543", "(503) 234-5678", "(212) 123-4567", "(416) 123-4567"]
let numberOf503

 numberOf503 = phoneNumbers.reduce((count, number) => { 
  if (number.slice(0, 5) === "(503)" ) {
   return ++count
  }
  return count
 },
0)