D3.js nest.map() Function

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nest.map() function in D3.js is used to form a nested map. The map contains a key-value pair determined by the key function which was executed very first. If no keys are declared or defined than map function returns the original array as it is.

Syntax:

nest.map(array)

Parameters:

It takes the collection array as the input.

Return:

Below are a few examples of the above function

Example 1:

When keys are defined.

<!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> 
    // Forming the collection 
    let coll=[ 
      {val:"val10", data:"data11"}, 
      {val:"val20", data:"data22"}, 
      {val:"val30", data:"data33"}, 
      {val:"val40", data:"data44"} 
    ] 
    let data= d3.nest() 
                .key(function(d) { 
      return d.val; }) 
                .map(coll) 
    // Logging the data 
    console.log(data); 
  </script> 
</body> 
</html> 

Output:

Example 2:

When no keys are defined.

<!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:"val10", data:"data11"}, 
      {val:"val20", data:"data22"}, 
    ] 
    //no keys are defined 
    let data= d3.nest() 
                .map(collection) 
    console.log(data); 
  </script> 
</body> 
</html> 

Output:

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