# Array to Object for loop type error - JS

**URL:** <https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923>\
**Category:** General\
**Created:** [March 31, 2020, 3:07am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923 "2020-03-31T03:07:45Z")\
**Posts on this page:** 14\
**Page:** 1

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [March 31, 2020, 3:07am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/1 "2020-03-31T03:07:45Z")

</div>

Hello all,

I’m working on a repl.it program for Code Platoon.  
The directions are:

> The variable tableData below represents data as it might appear in a table or spreadsheet. The first array contains column names and the rest of the arrays are rows of data. Write a function convertTable that converts the data in a nested array like tableData to an array of objects that matches the output below. Your function should work for any array formatted like tableData, meaning it should always use the first array given as the keys and the rest of the arrays as values.

> For example:

```auto
const tableData = [
  ["first_name", "last_name", "city", "state"],
  ["Elisabeth", "Gardenar", "Toledo", "OH"],
  ["Jamaal", "Du", "Sylvania", "OH"],
  ["Kathlyn", "Lavoie", "Maumee", "OH"]
]

convertTable(tableData) 

// The return is below
[
  { first_name : "Elisabeth", last_name : "Gardenar", city: "Toledo", state : "OH" },
  { first_name : "Jamaal", last_name : "Du", city: "Sylvania", state : "OH" },
  { first_name : "Kathlyn", last_name : "Lavoie", city: "Maumee", state : "OH" }
]

```

My program:

```auto
// Write your convertTable function here

const tableData = [
  ["first_name", "last_name", "city", "state"],
  ["Elisabeth", "Gardenar", "Toledo", "OH"],
  ["Jamaal", "Du", "Sylvania", "OH"],
  ["Kathlyn", "Lavoie", "Maumee", "OH"]
];

var row =[];

function convertTable(arr) {
  for (i = 0; i < arr.length; i++) {
    var fname = arr[i+1][0], lname = arr[i+1][1], city = arr[i+1][2], state = arr[i+1][3];
    console.log(arr[0][0] + " : \"" + fname + "\", " + arr[0][1] + " : \"" + lname + "\", " + arr[0][2] + " : \"" + city + "\", " + arr[0][3] + " : \"" + state + "\"");
         row = (arr[0][0] + " : \"" + fname + "\", " + arr[0][1] + " : \"" + lname + "\", " + arr[0][2] + " : \"" + city + "\", " + arr[0][3] + " : \"" + state + "\"");
  }    
  return row;
}
convertTable(tableData);

```

The console error:  
Native Browser JavaScript

first\_name : “Elisabeth”, last\_name : “Gardenar”, city : “Toledo”, state : “OH”  
first\_name : “Jamaal”, last\_name : “Du”, city : “Sylvania”, state : “OH”  
first\_name : “Kathlyn”, last\_name : “Lavoie”, city : “Maumee”, state : “OH”  
TypeError: Cannot read property ‘0’ of undefined  
at convertTable:14:27  
at eval:20:1  
at eval  
at new Promise

Thanks for your help in advance!!!

---

<div class="post-metadata">

**Author:** ![davidmarccram](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/davidmarccram/32/135975_2.png) [@davidmarccram](https://forum.freecodecamp.org/u/davidmarccram)\
**Post date:** [March 31, 2020, 4:09am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/2 "2020-03-31T04:09:53Z")

</div>

```auto
// This probably isn't exactly right but it is kind of close and I had fun trying
//It runs but the result is ordered a little differently than I expected
// So hopefully it helps a little bit

const tableData = [
  ["first_name", "last_name", "city", "state"],
  ["Elisabeth", "Gardenar", "Toledo", "OH"],
  ["Jamaal", "Du", "Sylvania", "OH"],
  ["Kathlyn", "Lavoie", "Maumee", "OH"]
];

function convertTable(arr) {
let keys=[];
let result = [];
//loop through the first element to get the key names you will use when you create your objects
for (let keyLoop = 0; keyLoop < tableData[0].length; keyLoop++) {
  keys.push(tableData[0][keyLoop]);  
}

//Loop for each record (Skipping index of 0 since that was keys)
for (let dataLoop = 1; dataLoop < tableData.length; dataLoop++) {
  let obj = {}; //
  //Assign values to each key
  for (let item in keys) {
  obj[keys[item]] = tableData[dataLoop][item];
  }
  result.push(obj); //update the array with the value for the currrent record
}
  return result; //return the final array
}
convertTable(tableData);

```

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [March 31, 2020, 6:09am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/3 "2020-03-31T06:09:02Z")

</div>

Thanks. That’s pretty creative and I’m having fun with this exercise too. I’ll play around with your suggestion and see if I can get it to work as expected.

However, I wasn’t looking for a solution, rather an explanation as to why i’m getting the type error on my variables. Do you know why?

---

<div class="post-metadata">

**Author:** ![ILM](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/ilm/32/363239_2.png) [@ILM](https://forum.freecodecamp.org/u/ILM)\
**Post date:** [March 31, 2020, 7:31am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/4 "2020-03-31T07:31:39Z")

</div>

you created a string, they want an object  
your row is NOT an object

you are almost there, that’s for sure, but you need to make it an object, not a string

after that try to make it work with arrays of any length, that I think also you are missing, you will need to tweak a few things there

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [March 31, 2020, 11:52pm UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/5 "2020-03-31T23:52:56Z")

</div>

Thanks. ieahleen, this is helpful. I will work on returning an Object. I did try using i values in every key value pair, but when I do that I get an infinate loop warning. That’s why I chose to use hard coded key value pairs. Do you have any tips or references I can read through on how to turn an array into an object. I’ve tried assign and create, but I cant use the array key value pairs or variable to create the Object (or at least I don’t know how). Thanks

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [April 1, 2020, 12:02am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/7 "2020-04-01T00:02:14Z")

</div>

Thanks, Randell, I appreciate the suggestion. However, I need the values to appear in exact order (first name: username, last name: user Lname, city: city name, state: state name). In his example, they don’t always show in the correct order. Any suggestions on that?

---

<div class="post-metadata">

**Author:** ![bbsmooth](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/bbsmooth/32/203556_2.png) [@bbsmooth](https://forum.freecodecamp.org/u/bbsmooth)\
**Post date:** [April 1, 2020, 12:23am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/9 "2020-04-01T00:23:43Z")

</div>

If you are truly concerned about order then you could use a Map which will iterate over the key/value pairs in the order you inserted them.

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [April 1, 2020, 12:27am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/10 "2020-04-01T00:27:19Z")

</div>

Thanks again Randell. Technically speaking it wouldn’t matter, but the instructions tell me the data needs to be displayed in that order. I’m still going to try to pass the exercise with the example provided though and see how it goes, but first I have to get the result to return correclty. One of the reasons I tried to avoid using @davidmarccram example is because I am learning and really would like explination and suggestion, so I can figure out what I’m doing wrong, not answers.

Either way, I’ve used his example but I’m getting an empty array returned. Here is my code:

```auto
// Write your convertTable function here

const tableData = [
  ["first_name", "last_name", "city", "state"],
  ["Elisabeth", "Gardenar", "Toledo", "OH"],
  ["Jamaal", "Du", "Sylvania", "OH"],
  ["Kathlyn", "Lavoie", "Maumee", "OH"]
];

var rowObj = {};

function convertTable(arr) {
  let keys = [];
  let result = [];
  
  for (let key = 0; key < tableData[0].length; key++) {
    keys.push(tableData[0][key]);
    console.log(keys);
  }
  
  for (let user = 1; user < keys.length; user++) {
    let tableObj = {};
    
    for (let item in keys) {
      tableObj[keys[item]] = tableData[user][item];
    }
    result.push[tableObj];
    console.log(tableObj);
  }
  return result;
}
convertTable(tableData);

```

and here is the console log window of results:

```auto
Native Browser JavaScript
   
['first_name']
['first_name', 'last_name']
['first_name', 'last_name', 'city']
['first_name', 'last_name', 'city', 'state']
{ first_name: 'Elisabeth',
  last_name: 'Gardenar',
  city: 'Toledo',
  state: 'OH' }
{ first_name: 'Jamaal',
  last_name: 'Du',
  city: 'Sylvania',
  state: 'OH' }
{ first_name: 'Kathlyn',
  last_name: 'Lavoie',
  city: 'Maumee',
  state: 'OH' }
=> []
   

```

I did try moving the let tableObj = {} outside of the function so it would be available outside of the loop and returing the tableObj, but this only returns one user. I also must return an array of objects not just an array.

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [April 1, 2020, 1:23am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/12 "2020-04-01T01:23:49Z")

</div>

Ah thanks! He used brackets instead of parentheses. I changed that and the array of all 3 objects did return correctly. Thanks to all three of you for your continued help!

When I run the tests to pass the assignment though it fails and here is what I get:

> Failed tests  
> handles\_given\_input  
> Your convertTable function didn’t produce the expected output  
> Expected $[0].first\_name = ‘Kathlyn’ to equal ‘Elisabeth’. Expected $[0].last\_name = ‘Lavoie’ to equal ‘Gardenar’. Expected $[0].city = ‘Maumee’ to equal ‘Toledo’.  
> More info  
> handles\_custom\_input

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [April 1, 2020, 1:26am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/13 "2020-04-01T01:26:43Z")

</div>

My assumption is that they want me to return the objects using Object dot notation instead of returning it in an array. Does that sound right?

Oh and the brackets was my mistake not his.

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [April 1, 2020, 2:23am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/15 "2020-04-01T02:23:15Z")

</div>

Yes it does look like it’s returing what’s expected, but the assignment test says it is not what’s expected. What I meant is maybe printing the lines using result.values or Object.values()

I suppose I’ll just go back to what I had in the beginning and work from there since this is not what the assignment wants.

I do appreciate everyone’s help,

---

<div class="post-metadata">

**Author:** ![klbellware](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/klbellware/32/139685_2.png) [@klbellware](https://forum.freecodecamp.org/u/klbellware)\
**Post date:** [April 1, 2020, 2:40am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/17 "2020-04-01T02:40:23Z")

</div>

Thanks for teaching me Randell. I discovered the reason the assignment wasn’t passing. I had moved let tableObj = { } outside of the function when I was getting an empty array. The empty array was due to the brakets after push instead of parentheses. Then I forgot to move it back . That was causing the loop to produce the same user each time through the loop instead of individule users. This clears the first part of my assignment. The second part just needs me to create another object that will produce similar results with different data. I know how to do that. So all is good! Thanks again.

---

<div class="post-metadata">

**Author:** ![davidmarccram](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/davidmarccram/32/135975_2.png) [@davidmarccram](https://forum.freecodecamp.org/u/davidmarccram)\
**Post date:** [April 1, 2020, 5:12am UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/18 "2020-04-01T05:12:31Z")

</div>

Glad you figured it out. It was really bugging me that something was a little off in the example I posted earlier. The discussion on this was really helpful to me too. Thanks, everyone.

---

<div class="post-metadata">

**Author:** ![ILM](https://sea3.discourse-cdn.com/freecodecamp/user_avatar/forum.freecodecamp.org/ilm/32/363239_2.png) [@ILM](https://forum.freecodecamp.org/u/ILM)\
**Post date:** [June 1, 2021, 7:00pm UTC](https://forum.freecodecamp.org/t/array-to-object-for-loop-type-error-js/365923/19 "2021-06-01T19:00:30Z")

</div>

Closed on June 1, 2021, 7:00pm UTC