map

Map

• An intermediary operation

• it keeps all the elements

  • the cardinalty of inputs/domain equals the cardinality of outputs/range

• similar to the data structure (objects that store key value pairs)

  • it is a noun

• One set of things is being mapped to a differnt set of things

• It is a verb

  • a function maps an array of values to another array of values.

• Say you have a function f and an array of values A = [a1, a2, a3, a4]. To map f over A means applying f to every element in A:

  • a1 → f (a1) = a1’

  • a2 → f (a2) = a2’

  • a3 → f (a3) = a3’

  • a4 → f (a4) = a4’

  • then assembling an array of the results in the same order as the inputs:

    • A’ = map( f, A ) = [a1’, a2’, a3’, a4’]

• A way of removing loops

  • use of streams in java and fluent interfaces to implement actions on elements in a data structure

Flatmap

• It is doing two opertaions

  • flatten

    • turn array of array into one array

  • map