Groups elements of an array into an object, using a key-generating function.
Examples: groupBy(['Hello', 'World', 'Hello'], a => a) // { Hello: ['Hello', 'Hello'], World: ['World'] }
The array to group
Function to generate a key for each element
An object mapping keys to arrays of grouped elements
Groups elements of an array into an object, using a key-generating function.
Examples: groupBy(['Hello', 'World', 'Hello'], a => a) // { Hello: ['Hello', 'Hello'], World: ['World'] }