Python-3.4.3/C3/Getting-started-with-arrays/English-timed

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 - shapearange, reshapeidentity 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.

Contributors and Content Editors

PoojaMoolya, Pratik kamble