Tips for effectively creating a fresh array of objects by extracting distinct values from arrays of child elements within a collection of parent objects

Question

Tips for effectively creating a fresh array of objects by extracting distinct values from arrays of child elements within a collection of parent objects

We have a requirement to extract data from objects structured like this:

[ { "first": 
    { "children" : [{ "name": "abc", "detail":"123"},
                  { "name": "def", "detail":"456"}
                 ]
    }},
  { "second": 
    { "children" : [{ "name": "ghi", "detail":"123"},
                  { "name": "jkl", "detail":"456"}
                 ]
    }},
  { "third": 
    { "children" : [{ "name": "mno", "detail":"123"},
                  { "name": "pqr", "detail":"456"}
                 ]
    }},
  { "fourth": 
    { "children" : [{ "name": "stu", "detail":"123"},
                  { "name": "vwx", "detail":"456"}
                 ]
    }},
  { "fifth": 
    { "children" : [{ "name": "yz", "detail":"123"},
                  { "name": "abc", "detail":"456"}
                 ]
    }},
  { "sixth": 
    { "children" : [{ "name": "def", "detail":"123"},
                  { "name": "ghi", "detail":"456"}
                 ]
    }}
]

Our objective is to generate a flattened array containing unique values extracted from the "name" field of each child object. The resulting array should look like this:

[{"value":"abc", "label":"abc"},
 {"value":"def", "label":"def"},
 {"value":"ghi", "label":"ghi"},
 {"value":"jkl", "label":"jkl"},
 {"value":"mno", "label":"mno"},
 {"value":"pqr", "label":"pqr"},
 {"value":"stu", "label":"stu"},
 {"value":"vwx", "label":"vwx"},
 {"value":"yz", "label":"yz"}
]

The provided code achieves the desired result, but it may not be the most efficient as it requires several passes over the array:

[
  ...new Set(
     [].concat.apply([], bases.map((base) => {
       if (!base.children || base.children.length === 0) return;
       return  base.children}
     )).map((child) => child.name)
  )
].map((optName) => {return {value: optName, label: optName};})

We are exploring alternative methods to achieve the same outcome without performing multiple iterations on the array. If you have any suggestions or optimizations, please share them.

javascript arrays ecmascript-6

Answer 1

Answer №1

Firstly, it's generally best practice not to focus on performance optimization until it becomes necessary.

Secondly, when chaining array prototype functions like map, forEach, or filter, multiple iterations are inherently part of the design.

Thirdly, there's no clear disadvantage to multiple iterations compared to a single iteration if the tasks performed in each iteration remain consistent. Tasks such as incrementing an index and comparing it with array length won't significantly impact performance when other operations involve pushing objects into arrays or checking set entries.

Here is a more streamlined code snippet for extracting unique names from an array:

let bases = [{
    children: [{
        name: "abc",
        detail: "123"
      },
      {
        name: "def",
        detail: "456"
      }
    ]
  }, {
    children: [{
        name: "abc" ,
        detail: "123"
      },
      {
        name: "xyz" ,
        detail: "456"
      }
    ]
  },
  {}
];

let output = bases
  .flatMap(b => b.children || [])
  .map(c => c.name)
  .filter((v, i, a) => a.indexOf(v) === i) // filter unique values
  .map(name => ({
    value: name,
    label: name,
  }));
  
console.log(output);

If you prefer to achieve all this in a single iteration, although less readable, it's also possible:

let bases = [{
    children: [{
        name: "abc",
        detail: "123"
      },
      {
        name: "def",
        detail: "456"
      }
    ]
  }, {
    children: [{
        name: "abc" ,
        detail: "123"
      },
      {
        name: "xyz" ,
        detail: "456"
      }
    ]
  },
  {}
];

let output = [];
let seenNames = {};
for (base of bases) {
  if (!base.children)
    continue;
  for (child of base.children) {
    let name = child.name;
    if (seenNames[name])
      continue;
    seenNames[name] = true;
    output.push({
      value: name,
      label: name,
    });
  }
}
  
console.log(output);

Answer 2

Firstly, it's generally best practice not to focus on performance optimization until it becomes necessary.

Secondly, when chaining array prototype functions like map, forEach, or filter, multiple iterations are inherently part of the design.

Thirdly, there's no clear disadvantage to multiple iterations compared to a single iteration if the tasks performed in each iteration remain consistent. Tasks such as incrementing an index and comparing it with array length won't significantly impact performance when other operations involve pushing objects into arrays or checking set entries.

Here is a more streamlined code snippet for extracting unique names from an array:

let bases = [{
    children: [{
        name: "abc",
        detail: "123"
      },
      {
        name: "def",
        detail: "456"
      }
    ]
  }, {
    children: [{
        name: "abc" ,
        detail: "123"
      },
      {
        name: "xyz" ,
        detail: "456"
      }
    ]
  },
  {}
];

let output = bases
  .flatMap(b => b.children || [])
  .map(c => c.name)
  .filter((v, i, a) => a.indexOf(v) === i) // filter unique values
  .map(name => ({
    value: name,
    label: name,
  }));
  
console.log(output);

If you prefer to achieve all this in a single iteration, although less readable, it's also possible:

let bases = [{
    children: [{
        name: "abc",
        detail: "123"
      },
      {
        name: "def",
        detail: "456"
      }
    ]
  }, {
    children: [{
        name: "abc" ,
        detail: "123"
      },
      {
        name: "xyz" ,
        detail: "456"
      }
    ]
  },
  {}
];

let output = [];
let seenNames = {};
for (base of bases) {
  if (!base.children)
    continue;
  for (child of base.children) {
    let name = child.name;
    if (seenNames[name])
      continue;
    seenNames[name] = true;
    output.push({
      value: name,
      label: name,
    });
  }
}
  
console.log(output);

Answer 3

Answer №2

To achieve a flattened representation of data with unique values and new object mappings, consider utilizing the Array#flatMap method in JavaScript.

var data = [{ first: { children: [{ name: "abc", detail: "123" }, { name: "def", detail: "456" }] } }, { second: { children: [{ name: "ghi", detail: "123" }, { name: "jkl", detail: "456" }] } }, { third: { children: [{ name: "mno", detail: "123" }, { name: "pqr", detail: "456" }] } }, { fourth: { children: [{ name: "stu", detail: "123" }, { name: "vwx", detail: "456" }] } }, { fifth: { children: [{ name: "yz", detail: "123" }, { name: "abc", detail: "456" }] } }, { sixth: { children: [{ name: "def", detail: "123" }, { name: "ghi", detail: "456" }] } }],
    result = Array.from(
        new Set(data
            .flatMap(Object.values)
            [...]
        ),
        value => ({ value, label: value })
    );

console.log(result);

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

Answer 4

To achieve a flattened representation of data with unique values and new object mappings, consider utilizing the Array#flatMap method in JavaScript.

var data = [{ first: { children: [{ name: "abc", detail: "123" }, { name: "def", detail: "456" }] } }, { second: { children: [{ name: "ghi", detail: "123" }, { name: "jkl", detail: "456" }] } }, { third: { children: [{ name: "mno", detail: "123" }, { name: "pqr", detail: "456" }] } }, { fourth: { children: [{ name: "stu", detail: "123" }, { name: "vwx", detail: "456" }] } }, { fifth: { children: [{ name: "yz", detail: "123" }, { name: "abc", detail: "456" }] } }, { sixth: { children: [{ name: "def", detail: "123" }, { name: "ghi", detail: "456" }] } }],
    result = Array.from(
        new Set(data
            .flatMap(Object.values)
            [...]
        ),
        value => ({ value, label: value })
    );

console.log(result);

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

Tips for effectively creating a fresh array of objects by extracting distinct values from arrays of child elements within a collection of parent objects

Answer №1

Answer №2

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