GroupBy

Description:

Grouping operators return collections of the source elements grouped by some algorithm. This method provides the ability to organise information into groups. you can specify a key based on the data held in a collection. The source data is then segregated into several iterable lists, each containing all of the items with a matching key. For example, you may group a collection of stock items by their categories. The result is a group of collections, one for each unique category, each containing all of the products in that category. Grouping of data has many uses. You may decide to group a large data set and display one group at a time through the user interface. You may also group the information so that you can aggregate the data, obtaining sums, averages or other aggregations for each group.

Note that there is an optional argument, named comparer at the end of arguments list, which accepts a function to make keys comparison customizable.

Samples:

let stock = [
  { name: 'Apple', category: 'Fruit', price: 0.30 },
  { name: 'Banana', category: 'Fruit', price: 0.35 },
  { name: 'Orange', category: 'Fruit', price: 0.29 },
  { name: 'Cabbage', category: 'Vegetable', price: 0.49 },
  { name: 'Carrot', category: 'Vegetable', price: 0.29 },
  { name: 'Lettuce', category: 'Vegetable', price: 0.30 },
  { name: 'Milk', category: 'Dairy', price: 1.12 }
];

let groups = stock.asEnumerable()
  .groupBy(
    s => s.category, //key selector
    s => s.name, //element selector
    (key, elements) => key + " : " + "[" + elements.join(",") + "]")//result selector
  .toArray();

console.log("*** using groupBy method to group category property ...");
for (let index = 0; index < groups.length; index++)
  console.log(groups[index]);