JavaScript: Group by groupName and Count Unique Names in an Array of Objects

This JavaScript code snippet demonstrates how to group an array of objects by 'groupName' and count the number of unique 'name' values within each group.

let arr = [
  {
    name: 'm1',
    groupName: 'group1',
    type: 'Messense_Mutation'
  },
  {
    name: 'm1',
    groupName: 'group2',
    type: 'Messense_Mutation'
  },
  {
    name: 'm1',
    groupName: 'group3',
    type: 'Messense_Mutation'
  },
  
  {
    name: 'm1',
    groupName: 'group7',
    type: 'Messense_Mutation',
    showValue: '414141',
    value: 0.21,
  },
  
  {
    name: 'm1',
    groupName: 'group4',
    type: 'Multi_Hit',
    showValue: '313131',
    value: 0.03,
  },
  {
    name: 'm2',
    groupName: 'group1',
    type: 'Frame_Shit_del',
    showValue: '444',
    value: 0.89,
  },
  {
    name: 'm2',
    groupName: 'group2',
    type: 'Splite_Site',
    showValue: '555',
    value: 0.42,
  },
  {
    name: 'm2',
    groupName: 'group3',
    type: 'Nonsense_Mutation',
    showValue: '666',
    value: 0.78,
  },
  {
    name: 'm2',
    groupName: 'group4',
    type: 'Frame_Shit_del',
    showValue: '777',
    value: 0.23,
  },
  {
    name: 'm5',
    groupName: 'group4',
    type: 'Splite_Site',
    showValue: '888',
    value: 0.56,
  }
]

const groupByName = {};
arr.forEach(obj => {
  if (groupByName[obj.groupName]) {
    groupByName[obj.groupName].push(obj.name);
  } else {
    groupByName[obj.groupName] = [obj.name];
  }
});

for (let groupName in groupByName) {
  const names = groupByName[groupName];
  const uniqueNames = [...new Set(names)];
  console.log(`Group ${groupName} has ${uniqueNames.length} names: ${uniqueNames.join(', ')}`);
}

// Output:
// Group group1 has 2 names: m1, m2
// Group group2 has 2 names: m1, m2
// Group group3 has 2 names: m1, m2
// Group group7 has 1 names: m1
// Group group4 has 3 names: m1, m2, m5

Explanation:

1. Grouping: The code uses a forEach loop to iterate through the arr array. For each object obj, it checks if the groupName exists as a key in the groupByName object. If it does, it adds the obj.name to the existing array for that groupName. Otherwise, it creates a new array with obj.name as the first element.
2. Counting Unique Names: After grouping, the code loops through the groupByName object. For each groupName, it uses the Set object to get the unique names and then counts the length of the resulting array to get the number of unique names.
3. Output: The code outputs the results in the format Group groupName has count names: name1, name2, ....

Key Concepts:

• Array Iteration: Using forEach to iterate through an array of objects.
• Object Properties: Accessing and manipulating object properties using dot notation (e.g., obj.groupName).
• Sets: Utilizing Set to find unique elements in an array.
• Template Literals: Using backticks (`) to create formatted strings with embedded variables.

This code snippet effectively groups objects by a common property (groupName) and provides a clear and concise way to count the unique values of another property (name) within each group. It's a useful technique for data analysis and organization in JavaScript.