Difference between revisions of "Python/C3/Getting-started-with-arrays/English-timed"
From Script | Spoken-Tutorial
| Line 26: | Line 26: | ||
|- | |- | ||
| − | | | + | | 00:39 |
|Unlike lists, arrays cannot have heterogeneous data elements. | |Unlike lists, arrays cannot have heterogeneous data elements. | ||
Revision as of 15:48, 3 September 2014
| Time | Narration |
| 00:01 | Hello friends and welcome to the spoken tutorial on 'Getting started with arrays'. |
| 00:06 | At the end of this tutorial, you will be able to,
|
| 00:26 | So Before beginning this tutorial,we would suggest you to complete the tutorial on "Getting started with Lists". |
| 00:35 | Arrays are homogeneous data structures. |
| 00:39 | Unlike lists, arrays cannot have heterogeneous data elements. |
| 00:45 | They can have only one type of data as their entries, be them all integers, strings, or maybe floats, but not a mix. |
| 00:55 | Arrays of a given length are comparatively much faster in mathematical operations than lists of the same length, because of the fact that they are homogeneous data structures. |
| 01:07 | Let us see how to create arrays. |
| 01:11 | Run your IPython interpreter with space hypen pylab option, to load the required modules to work with arrays. |
| 01:21 | So type ipython space hypen pylab |
| 01:28 | To create an array we will use the function array() as,a1 = array within brackets square brackets 1 comma 2 comma 3 comma 4 |
| 01:45 | Notice that we created a one dimensional array here. |
| 01:49 | Also notice that the object we passed to create an array is a list. |
| 01:54 | Now let us see how to create a two dimensional array. |
| 01:58 | We create two dimensional array by converting a list of lists to an array as,
a2 = array within brackets within square brackets 1 comma 2 comma 3 comma 4 comma then again within square brackets 5 comma 6 comma 7 comma 8 and hit enter. |
| 02:38 | Now let us use arrange() function to create the same array as before. |
| 02:45 | For that type ar = arrange within bracket 1 comma 9 and hit enter,so type
print ar to get the output. |
| 03:02 | So now, As you can see, we obtained a one dimensional array with elements from 1 to 8. |
| 03:12 | Now can we make it a two dimensional array of order 2 by 4? Yes,we can. |
| 03:20 | For this we will have to use the function reshape() , |
| 03:24 | So type ar.reshape brackets 2 comma 4 and hit enter |
| 03:33 | So type ar.reshape within brackets 4 comma 2
then ar = ar dot reshape within brackets 2,4 |
| 03:55 | Hence,we got our two-dimensional array. |
| 03:58 | Now, let us see how to convert a list object to an array. |
| 04:02 | We define a list,say l1 |
| 04:07 | So type l1 = within square brackets 1 comma 2 comma 3 comma 4 and hit enter |
| 04:16 | Now to convert this list to an array,we use the array function as, a3 = array within brackets l1 |
| 04:30 | To find the shape of an array we can use the method dot shape , |
| 04:36 | let us check the shape of the arrays we have created so far, |
| 04:44 | a2 dot shape object is a tuple, and it returned a tuple (2 comma 4). |
| 04:52 | A tuple is nothing but an ordered list of elements. |
| 04:56 | So Pause the video here, try out the following exercise and resume the video. |
| 05:12 | Find out the shape of the other arrays i.e. a1 comma a3 comma ar that we have created. |
| 05:22 | It can be done as
a1 dot shape a3 dot shape ar dot shape in the terminal |
| 05:37 | Now let us try to create a new array with a mix of elements and see what will happen, |
| 05:45 | So type a4 = array within brackets then square bracket 1 comma 2 comma 3 comma and single quote a string and hit enter |
| 06:07 | Well, we would expect an error as it has been previously mentioned that arrays handle elements with the same data type, but it didn't raise an error. |
| 06:16 | Let us check the values in the new array created. |
| 06:19 | So Type a4 in the terminal, |
| 06:27 | Did you notice it, all the elements have been implicitly type casted as strings, though our first three elements were meant to be integers. |
| 06:37 | Also,if you have noticed,we got something like 'dtype S8' in the output. |
| 06:44 | dtype is nothing but the data type which is the minimum type required to hold the objects in the sequence. |
| 06:52 | Let us now move on to study functions like zeros() function and ones() function. |
| 06:59 | For this ,we will have to create a matrix. |
| 07:02 | let us see how to create an identity matrix of a given size, this is a two-dimensional array in which all the diagonal elements are ones and rest of the elements are zeros. |
| 07:13 | We can create an identity matrix using the function identity() . |
| 07:18 | The function identity() takes an integer argument which specifies the size of the desired matrix, |
| 07:27 | As you can see the identity function returned a three by three square matrix with all the diagonal elements as one and the rest of the elements as zeros. |
| 07:43 | So type identity within brackets 3 |
| 07:48 | zeros() function accepts a tuple, which is the order of the array that we want to create, and it generates an array with all elements as zeros. |
| 07:59 | Let us create an array of the order four by five with all the elements zero. |
| 08:06 | We can do it using the method zeros(), |
| 08:10 | So type zeros within brackets then again in bracket 4 comma 5 and hit enter |
| 08:21 | Notice that we passed a tuple to the function zeros. |
| 08:25 | Pause the video here, try out the following exercise and resume the video. |
| 08:33 | So now we learnt two functions identity and zeros |
| 08:38 | Find out about the functions |
| 08:41 | zeros underscore like() |
| 08:43 | ones() |
| 08:44 | ones underscore like() |
| 08:48 | Try the following, first check the value of a1, |
| 08:52 | We see that a1 is a single dimensional array, |
| 08:56 | So type a1 and hit enter |
| 09:01 | So next now try a1 into 2 |
| 09:05 | So type a1 into 2 |
| 09:09 | It returned a new array with all the elements multiplied by 2. |
| 09:13 | Now let us again check the contents of a1 |
| 09:19 | note that the value of a1 still remains the same. |
| 09:23 | Similarly with addition,so type a1 plus 2 and hit enter and then type a1 |
| 09:36 | it returns a new array, with all the elements summed with two. |
| 09:41 | But again notice that the value of a1 has not been changed. |
| 09:46 | You may change the value of a1 by simply assigning the newly returned array as,a1 space plus=2 |
| 10:03 | Notice the change in elements of a by typing 'a' so type a and hit enter |
| 10:13 | so type a1 to get the output |
| 10:18 | We can use all the mathematical operations with arrays, |
| 10:22 | Now let us try this a1 = arrays within brackets square brackets 1 comma 2 comma 3 comma 4
and hit enter |
| 10:45 | then a2 = array within brackets square brackets 1 comma 2 comma 3 comma 4
then type a1 + a2 and hit enter |
| 11:07 | This returns an array with element by addition |
| 11:15 | So try out a1 into a2 |
| 11:23 | a1 into a2 returns an array with element by element multiplication, |
| 11:31 | And notice that it does not perform matrix multiplication. |
| 11:37 | This brings us to the end of the end of this tutorial. |
| 11:41 | In this tutorial, we have learnt to,
1. Create an array using the array() function. |
| 11:46 | 2. Convert a list to an array. |
| 11:49 | 3. Perform some basic operations on arrays like addition,multiplication. |
| 11:53 | 4. Use functions like - .shape - arrange() - .reshape - zeros() & zeros underscore like() - ones() & ones underscore like() |
| 12:05 | Here are some self assessment questions for you to solve |
| 12:09 | 1.First one, x = array within brackets square bracket 1 comma 2 comma 3 comma square bracket 5 comma 6 comma 7 is a valid statement |
| 12:23 | So IS True or False? |
| 12:27 | 2. What does the ones underscore like() function do? |
| 12:31 | A. Returns an array of ones with the same shape and type as a given array. |
| 12:37 | B. Return a new array of given shape and type, filled with ones. |
| 12:43 | Now Read the statements and answer, |
| 12:47 | Only statement A is correct. |
| 12:49 | Only statement B is correct. |
| 12:51 | Both statement A and B are correct. |
| 12:53 | Both statement A and B are incorrect. |
| 12:56 | So let's find the answers, |
| 12:59 | 1. The answer is False. |
| 13:02 | The correct way would be to assign the elements as a list of lists and then convert it to an array |
| 13:10 | Type x = array within brackets square brackets 1 comma 2 comma 3 comma within brackets 5 comma 6 comma 7 |
| 13:21 | 1. The function ones underscores like() returns an array of ones with the same shape and type as a given array. |
| 13:29 | Hope you have enjoyed this tutorial and found it useful. |
| 13:31 | Thank you! |
