How to Map Array values from one Array to Another Array JavaScript?

Question

This is my Code. Where I want to Pass the Values of kvArray to Second Array.

var kvArray = [{key: 1, value: 10}, 
               {key: 2, value: 20}, 
               {key: 3, value: 30}];

var reformattedArray = kvArray.map(obj => { 
   var payload = {};
   payload["rt"];
   payload["do"];
   payload["f1"];
   payload[obj.key] = obj.value;
   console.log(payload["rt"]);
   return payload;
});

The console.log is coming undefined. Can anyone help here? I am pretty new to Map function.

I want to Print this result.

 payload["do"]=10
 payload["f1"]=20
 payload["f2"]=30

You are assigning payload[1], payload[2] and payload[3] when you are referring to obj.key in your map function. Thus payload["rt"] remains undefined. — Lesleyvdp
– Lesleyvdp, Commented Aug 29, 2018 at 7:29
btw, it's quite unclear, if the wanted keys depends on the index or on the key values. — Nina Scholz
– Nina Scholz, Commented Aug 29, 2018 at 8:17

NullPointer · Accepted Answer · 2018-08-29 08:17:37Z

4

var kvArray = [{key: 1, value: 10}, 
               {key: 2, value: 20}, 
               {key: 3, value: 30}];

var reformattedArray = kvArray.map(obj =>{ 
   var payload = {};
   const mapping = [null, 'rt', 'do', 'f1']; 
   const key = mapping[obj.key];
   payload[key] = obj.value;
   return payload;
});
console.log(reformattedArray);

edited Aug 29, 2018 at 8:17

NullPointer

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answered Aug 29, 2018 at 7:55

Andrey Davydov

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2 Comments

codemt Over a year ago

this is helpful:). thank you so much. Just to pass the keys of 'rt','do' to the payload, it is better to map them by declaring them in another array. thats sweet :)

Nurkartiko Over a year ago

const mapping = [null, 'rt', 'do', 'f1']; what is null for?

Nina Scholz · Accepted Answer · 2018-08-29 08:10:09Z

4

You could use a destructuring assignment and build a new object with computed property names.

For the final keys, you could use an object keys with corresopnding keys to the the keys of the given object.

var kvArray = [{ key: 1, value: 10 }, { key: 2, value: 20 }, { key: 3, value: 30 }],
    keys = { 1: 'rt', 2: 'do', 3: 'fi' },
    result = kvArray.map(({ key, value }) => ({ [keys[key]]: value }));
    
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Aug 29, 2018 at 8:10

answered Aug 29, 2018 at 7:50

Nina Scholz

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Comments

zoey0_0 · Accepted Answer · 2018-08-29 07:34:26Z

2

I'm not sure what format you want.

try the code below：

var kvArray = [{ key: 1, value: 10 },
  { key: 2, value: 20 },
  { key: 3, value: 30 }];
var reformattedArray = kvArray.map(obj => obj.value);
console.log(reformattedArray)

the result will be:

[ 10, 20, 30 ]

answered Aug 29, 2018 at 7:34

zoey0_0

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Comments

Eriks Klotins · Accepted Answer · 2018-08-29 07:32:06Z

0

Not sure what you are trying to achieve with lines:

payload["rt"];
payload["do"];
payload["f1"];

If you want to create new keys in the reformatterArray, try assigning a value, eg.

var kvArray = [{key: 1, value: 10}, 
           {key: 2, value: 20}, 
           {key: 3, value: 30}];
var reformattedArray = kvArray.map(obj =>{ 
   var payload = {};
   payload["rt"] = "";
   payload["do"]= "";
   payload["f1"]= "";
   payload[obj.key] = obj.value;
   console.log(payload["rt"]);
   return payload;
});

console.log(reformattedArray):
//result
0: {1: 10, rt: "", do: "", f1: ""}
1: {2: 20, rt: "", do: "", f1: ""}
2: {3: 30, rt: "", do: "", f1: ""}

answered Aug 29, 2018 at 7:32

Eriks Klotins

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Comments

Muhammad Osama · Accepted Answer · 2018-08-29 07:32:16Z

0

You were assigning the value to payload but getting the values of payload.

  var kvArray = [{key: 1, value: 10}, 
               {key: 2, value: 20}, 
               {key: 3, value: 30}];
var reformattedArray = kvArray.map(obj =>{ 
   var payload = {};
   payload[obj.key] = obj.value;
  console.log(payload[obj.key]);
   return payload;

});

answered Aug 29, 2018 at 7:32

Muhammad Osama

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Comments

Manasi · Accepted Answer · 2018-08-29 07:32:56Z

0

You are mapping data to reformattedArray , so you need to pring reformattedArray to get values,

   var kvArray = [{key: 1, value: 10}, 
               {key: 2, value: 20}, 
               {key: 3, value: 30}];
var reformattedArray = kvArray.map(obj =>{ 
   var payload = {};
   payload[obj.key] = obj.value;
   return payload;
});

  console.log(reformattedArray);

Also you have following code which is of no use

payload["rt"]; payload["do"]; payload["f1"];

answered Aug 29, 2018 at 7:32

Manasi

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1 Comment

codemt Over a year ago

i have defined the keys of the array payload. and i want this output payload["rt"] = 10. like this.

RAJA · Accepted Answer · 2018-08-29 07:49:05Z

0

This code works fine

let kvArray = [{key: 1, value: 10},
           {key: 2, value: 20},
           {key: 3, value: 30}];

let reformattedArray = kvArray.map(obj =>{
   var payload = {};
   payload[obj.key] = obj.value;
   return payload;
});

console.log(reformattedArray)

The above code print output like this

[
  0: {1: 10}
  1: {2: 20}
  2: {3: 30}
]

For more info, refer this link

edited Aug 29, 2018 at 7:49

answered Aug 29, 2018 at 7:41

RAJA

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