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#+TITLE: Getting started with arrays
#+AUTHOR: FOSSEE
#+EMAIL: info@fossee.in
#+DATE:    

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#+LANGUAGE:  en
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* Outline
  - Arrays
    - why arrays over lists
  - Creating arrays
  - Array operations

* Overview of Arrays
  - Arrays are homogeneous data structures.
    - elements have to the same data type
  - Arrays are faster compared to lists
    - at least /80-100 times/ faster than lists

* Creating Arrays
  - Creating a 1-dimensional array
  : In []: a1 = array([1, 2, 3, 4])
  ~[1, 2, 3, 4]~ is a list.
* Creating two-dimensional array
  - Creating a 2-dimensional array
  : In []: a2 = array([[1,2,3,4],[5,6,7,8]])
  here we convert a list of lists to an array making a 2-d array.
  - Using ~arange()~ function
  : In []: ar = arange(1,9)
* ~reshape()~ method
  - To reshape an array
  : In []: ar.reshape(2, 4)
  : In []: ar.reshape(4, 2)
  : In []: ar = ar.reshape(2, 4)

* Creating ~array~ from ~list~.
  - ~array()~ method accepts list as argument
  - Creating a list
   : In []: l1 = [1, 2, 3, 4]
  - Creating an array
    : In []: a3 = array(l1)

* Exercise 1
  Create a 3-dimensional array of the order (2, 2, 4).

* ~.shape~ of array
  - ~.shape~
    To find the shape of the array
    : In []: a2.shape
  - ~.shape~
    returns a tuple of shape
* Exercise 2
  Find out the shape of the other arrays(a1, a3, ar) that we have created.
* Homogeneous data
  - All elements in array should be of same type
    : In []: a4 = array([1,2,3,'a string'])
* Implicit type casting 
   : In []: a4
    All elements are type casted to string type
* ~identity()~, ~zeros()~ methods
  - ~identity(n)~
    Creates an identity matrix, a square matrix of order (n, n) with diagonal elements 1 and others 0.
  - ~zeros((m, n))~
    Creates an ~m X n~ matrix with all elements 0.

* Learning exercise
  - Find out about
    - ~zeros_like()~
    - ~ones()~
    - ~ones_like()~

* Array operations
  - ~a1 * 2~
    returns a new array with all elements of ~a1~ multiplied by ~2~.
    - Similarly ~+~, ~-~ \& ~/~.
  - ~a1 + 2~
    returns a new array with all elements of ~a1~ summed with ~2~.
  - ~a1 += 2~
    adds ~2~ to all elements of array ~a1~.
    - Similarly ~-=~, ~*=~ \& ~/=~.
  - ~a1 + a2~
    does elements-wise addition.
    - Similarly ~-~, ~*~ \& ~/~.
  - ~a1 * a2~
    does element-wise multiplication

  *Note* - array(A) * array(B) does element wise multiplication and not matrix multiplication

* Summary
  In this tutorial we covered,
  - Basics of arrays
  - Creating arrays
  - Arrays from lists
  - Basic array operations

* Thank you!
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  This spoken tutorial has been produced by the
  \textcolor{blue}{FOSSEE} team, which is funded by the 
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    \textcolor{blue}{National Mission on Education through \\
      Information \& Communication Technology \\ 
      MHRD, Govt. of India}.
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