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#+TITLE: Getting started with arrays

#+AUTHOR: FOSSEE

#+EMAIL: info@fossee.in

#+DATE:    

#+DESCRIPTION: 

#+KEYWORDS: 

#+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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