Python-3.4.3/C3/Getting-started-with-arrays/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Welcome to the spoken tutorial on Getting started with arrays. |
| 00:06 | In this tutorial, you will learn to,
Create arrays using data Create arrays from lists Perform basic array operations Create an identity matrix and Use the method zeros |
| 00:24 | To record this tutorial, I am using
Ubuntu Linux 16.04 operating system Python 3.4.3 and IPython 5.1.0 |
| 00:39 | To practice this tutorial, you should know how to use Lists.If not, see the relevant Python tutorials on this website. |
| 00:50 | Arrays are homogeneous data structures. All elements in it must be of same data type. |
| 00:58 | In this tutorial, we will be using numpy library which we used in earlier tutorial. |
| 01:05 | Let us first open the terminal by pressing Ctrl+Alt+T keys simultaneously. |
| 01:12 | Let us start ipython by typing ipython3 and press Enter. We can see the ipython prompt. |
| 01:22 | Now we will import numpy. Type, import numpy as np and press Enter. |
| 01:32 | Now let us see how to create arrays. |
| 01:36 | From here onwards, please remember to press the Enter key after typing every command on the terminal. |
| 01:44 | Type, a1 is equal to np dot array inside parentheses inside square brackets 1 comma 2 comma 3 comma 4 |
| 01:54 | Type a1 Notice that we have created a one dimensional array here. |
| 02:02 | Also notice that the object we passed to create an array is a list, i.e a1. |
| 02:09 | Next we will see how to create two dimensional array. |
| 02:14 | Two dimensional array is created by converting a list of lists to an array. |
| 02:20 | Type, a2 is equal to np dot array inside parentheses inside square brackets again inside square brackets 1 comma 2 comma 3 comma 4 comma inside square brackets 5 comma 6 comma 7 comma 8 |
| 02:38 | Type a2 This is our 2-dimensional array. |
| 02:44 | Next we will see about arange method. |
| 02:48 | To arrange the elements in an array we use arange method. The syntax is shown here. |
| 02:57 | Type ar is equal to np dot arange inside parentheses 1 comma 9. |
| 03:04 | Type print inside parentheses ar |
| 03:08 | Here, 1 is the start value and 9 is the stop value. |
| 03:13 | As you can see, we obtained a one dimensional array between 1 and 9 with 1 included and 9 excluded. |
| 03:22 | It will give the elements one less than the stop value. |
| 03:26 | Can we make a two dimensional array of order 2 by 4? Yes, we can do it. |
| 03:33 | We will use reshape method to change the shape of an array. |
| 03:38 | The syntax is: object.reshape inside parentheses rows comma columns |
| 03:45 | Switch back to the terminal. |
| 03:48 | Type, ar dot reshape inside parentheses 2 comma 4. |
| 03:54 | Type ar Shape of the original array ar is not changed. |
| 04:00 | If you want to change the shape of the original array, type ar dot shape is equal to inside parentheses 2 comma 4. |
| 04:11 | Type ar We can see that the shape of the original array ar is changed now. |
| 04:20 | To find the shape of an array we can use the method shape. |
| 04:25 | It returns a tuple of the shape of an array.
A tuple is nothing but an ordered list of elements. |
| 04:34 | Let us check the shape of the arrays we have created so far. |
| 04:38 | Type a2 dot shape a2.shape object is a tuple, and it returned a tuple (2, 4). |
| 04:47 | Pause the video here, try out the following exercise and resume the video. |
| 04:52 | Find out the shape of the arrays a1 and ar which we have created earlier in this tutorial. |
| 04:58 | Let us see the solution. Type, a1 dot shape |
| 05:04 | Since a1 is a single dimensional array, the column is empty. |
| 05:09 | Type, ar dot shape ar is a two dimensional array. |
| 05:15 | Now let us try to create a new array with elements of different datatypes. |
| 05:21 | Type a3 is equal to np dot array inside parentheses inside square brackets 1 comma 2 comma 3 comma inside single quotes a string |
| 05:33 | Arrays handle elements with the same datatype. |
| 05:37 | Here we are handling with different datatypes. So it should give us error. |
| 05:44 | Type a3 But we did not get any error. Because all the elements get implicitly converted as strings. |
| 05:54 | This is how array works. |
| 05:57 | Note that the output mentions dtype=’<U21' |
| 06:04 | A dtype is the datatype required to hold the objects in sequence. |
| 06:10 | The characters of dtype i.e. ’<U21' might differ with python version. |
| 06:17 | Next we will see about identity matrix. |
| 06:21 | It is a square matrix of order (n,n) with ones on the main diagonal and all other elements as zeros. |
| 06:29 | The syntax is identity inside parentheses n. |
| 06:34 | Let us see how to create a 2 by 2 identity matrix. |
| 06:39 | Type, np dot identity inside parentheses 2. |
| 06:45 | We can see all ones in the main diagonal as expected. |
| 06:50 | Next is Zeros method. |
| 06:53 | It creates an m by n matrix with all elements as 0. |
| 06:58 | The Syntax is: zeros inside parentheses inside parentheses m, n |
| 07:05 | Let us create an array of the shape (4, 5) with all the elements zero. |
| 07:11 | Type, np dot zeros inside parentheses inside parentheses 4 comma 5. |
| 07:18 | The default output of identity and zeros method are in float datatype. |
| 07:24 | Explore the below functions on your own:
zeros_like ones ones_like |
| 07:34 | Try the following. |
| 07:36 | First check the value of a1 which we assigned earlier. |
| 07:41 | Type a1 We see that a1 is a single dimensional array. |
| 07:48 | Let us now try a1 multiplied by 2 It returned a new array with all the elements multiplied by 2. |
| 07:58 | Now let us again check the contents of a1. Note that the value of a1 still remains the same. |
| 08:06 | Similarly we will try with addition. |
| 08:10 | Type, a1 plus 2 It returns a new array, with all the elements summed with two. |
| 08:18 | Type a1 . But again notice that the value of a1 has not been changed. |
| 08:26 | Let us try with a1 plus equal to 2 |
| 08:31 | Type, a1 This will change the array a1 itself as we are assigning the new output to a1. |
| 08:41 | We can use all the mathematical operations with arrays. Next, we will see how to add two arrays. |
| 08:50 | Type, a1 is equal to np dot array inside parentheses inside square brackets 1, 2, 3, 4 |
| 09:00 | Type a2 is equal to np dot array inside parentheses inside square brackets 5, 6, 7, 8 |
| 09:10 | Type a1 plus a2This returns an array by adding element by element. |
| 09:18 | Type a1 multiplied by a2 It returns an array with element by element multiplication. |
| 09:27 | This brings us to the end of the end of this tutorial. |
| 09:31 | In this tutorial, we have learnt to,
1. Create an array using the array() function. 2. Perform some basic operations on arrays like addition and multiplication. 3. Use methods like - shape , arange, reshape, identity andzeros |
| 09:50 | Here is a self assessment question for you to solve |
| 09:54 | x is equal to np.array inside parentheses inside square brackets 1, 2, 3, inside square brackets 5, 6, 7 is a valid statement?
True False |
| 10:10 | And the answer is False. |
| 10:13 | The correct way is to assign the elements as a list of lists and then convert it to an array. |
| 10:19 | That is x is equal to np.array inside parentheses inside square brackets again inside square brackets 1, 2, 3, inside square brackets 5, 6, 7 |
| 10:35 | Please post your timed queries in this forum. |
| 10:39 | Please post your general queries on Python in this forum. |
| 10:44 | FOSSEE team coordinates the TBC project. |
| 10:48 | Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India.For more details, visit this website. |
| 10:57 | This is Priya from IIT Bombay signing off. Thanks for watching. |
