D3.js nest.key() Function

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nest.key() function in D3.js is used to register a new key function which is invoked for each element in the input array. Whenever a new key is registered, it is then pushed in the array to the end.

Syntax:

nest.keys(key)

Parameters:

It takes only one parameter i.e the key function.

Return: It returns a string identifier.

Below given are few examples that explain the function in a better way.

Example 1:

<!DOCTYPE html> 
<html lang="en"> 
<head> 
  <meta charset="UTF-8"> 
  <meta name="viewport" 
        content="width=device-width,  
                 initial-scale=1.0"> 
  <title>Document</title> 
</head> 
<style> 
  .originalColor{ 
    height: 100px; 
    width: 100px; 
  } 
  .darkerColor{ 
    height: 100px; 
    width: 100px; 
  } 
</style> 
<body> 
    
  <!-- Fetching from CDN of D3.js -->
  <script type = "text/javascript" 
          src =  
"https://d3js.org/d3.v4.min.js"></script> 
  <script> 
    let collection=[ 
      {val:"val1"}, 
      {val:"val2"}, 
      {val:"val3"}, 
      {val:"val4"} 
    ] 
    let data=d3.nest().key((d)=>{return d.val}) 
                      .entries(collection) 
    console.log(data); 
  </script> 
</body> 
</html> 

Output:

Example 2:

<!DOCTYPE html> 
<html lang="en"> 
<head> 
  <meta charset="UTF-8"> 
  <meta name="viewport" 
        content="width=device-width, 
                 initial-scale=1.0"> 
  <title>Document</title> 
</head> 
<style> 
  .originalColor{ 
    height: 100px; 
    width: 100px; 
  } 
  .darkerColor{ 
    height: 100px; 
    width: 100px; 
  } 
</style> 
<body> 
    
  <!--fetching from CDN of D3.js -->
  <script type = "text/javascript"
          src =  
"https://d3js.org/d3.v4.min.js"> 
   </script> 
  <script> 
    let collection=[ 
      {val:"val1", data:"data1", anotherData:"data1"}, 
      {val:"val2", data:"data2", anotherData:"data2"}, 
      {val:"val3", data:"data3", anotherData:"data3"}, 
      {val:"val4", data:"data4", anotherData:"data4"} 
    ] 
    //key is added 
    let data=d3.nest().key((d)=>{return d.val}) 
                      //another key is nested and added 
                      .key((d)=>{return d.data}) 
                      //another key is added and nested 
                      .key((d)=>{return d.anotherData}) 
                      .entries(collection) 
    console.log(data); 
  </script> 
</body> 
</html> 

Output:

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