Python-3.4.3/C2/Loading-Data-From-Files/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Hello friends and welcome to the spoken tutorial on "loading data from files". |
| 00:07 | In this tutorial, you will learn to:
read data from files which contain data in: single column format or multiple columns separated by spaces or other delimiters. |
| 00:21 | To record this tutorial, I am using:
Ubuntu Linux 14.04 operating system, Python 3.4.3, IPython 5.1.0. |
| 00:37 | You should know how to run basic Python commands on the ipython console. |
| 00:43 | If not, for relevant Python tutorials, please visit this website. |
| 00:49 | Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously. Now, type ipython3 and press Enter. |
| 01:02 | Let us initialise the pylab package.
Type percent pylab and press Enter. |
| 01:12 | Let us begin with reading the file primes.txt. This file contains a list of prime numbers listed in a column. |
| 01:22 | Type: cat(space)primes(dot)txt |
| 01:29 | We can use the cat command to fetch data from the file and display it on the terminal. Press Enter. |
| 01:38 | We see the prime numbers are displayed on the terminal. |
| 01:43 | Now we can use the loadtxt() command to store this list into the variable primes. |
| 01:50 | So, type: primes(equal to)loadtxt(within parentheses)(within double quotes)primes(dot)txt and press Enter. |
| 02:07 | Please make sure that you provide the correct path to the file, 'primes.txt'. |
| 02:13 | The file, in our case, is present in the home folder. |
| 02:18 | primes is now a sequence of prime numbers that was listed in the file primes.txt. |
| 02:25 | Now let us display the contents in the variable primes. |
| 02:29 | So, type: print (within parentheses) primes and press Enter. We see the sequence printed. |
| 02:41 | We observe that all the numbers end with a period ‘.’ . This is because all these numbers are floats. |
| 02:51 | Now, type: cat(space)pendulum(dot)txt and press Enter. |
| 03:01 | This file contains two columns of data. This first column contains the length of the pendulum.
The second column contains the corresponding time period. |
| 03:15 | Let us now read the data from the file into the variable pend using the loadtxt command. |
| 03:23 | So, type: pend(equal to)loadtxt(within parentheses)(within double quotes)pendulum(dot)txt and press Enter. |
| 03:39 | Please note that loadtxt needs both the columns of the file to have equal number of rows. |
| 03:47 | Now, print the variable pend to see what it contains.
Type: print(within parentheses)pend and press Enter. |
| 04:00 | Notice that the variable has two sequences containing two columns of the data file. |
| 04:07 | Let us use an additional argument of the loadtxt command to read the data into two separate sequences. |
| 04:16 | So, type L(comma)T(equal to)loadtxt(within parentheses within double quotes)pendulum(dot)txt(after double quotes comma)unpack(equal to)True
and press Enter. |
| 04:42 | Now print the variables L and T to see what they contain. |
| 04:47 | Type: print(within parentheses)L and press Enter.
Type: print(within parentheses)T and press Enter. |
| 05:01 | Notice, that L and T now contain the first and second columns of data from the pendulum.txt respectively. |
| 05:12 | unpack(equal to)True has made the two columns into two separate and simple sequences. |
| 05:20 | Pause the video over here and try out the following exercise and resume the video. |
| 05:27 | Read the data from the file pendulum(underscore)semicolon(dot)txt. |
| 05:33 | This file contains data in two columns. These columns are separated by semicolons.
Use the IPython help to see how to do this. |
| 05:45 | Let us look at the solution. Switch to the terminal. |
| 05:50 | First we will see the content of the file. |
| 05:54 | So, type: cat space pendulum(underscore)semicolon(dot)txt and press Enter. We see the two columns separated by a semicolon. |
| 06:12 | Now, type: L(comma)T(equal to)loadtxt (within parentheses within double quotes) pendulum(underscore)semicolon (dot)txt(after double quotes comma)unpack(equal to)True(comma)delimiter(equal to)(within double quotes)semicolon.
And press Enter. |
| 06:48 | Now, print(within parentheses)L and press Enter.
print(within parentheses)T and press Enter. |
| 07:03 | This will display the contents inside the two variables L and T. |
| 07:09 | This brings us to the end of this tutorial. In this tutorial, we have learnt to read data from files using the loadtxt() command. |
| 07:20 | The data can be in:
a single column format or multiple column format, separated by spaces or other delimiters. |
| 07:31 | Here are some self assessment questions for you to solve.
1. loadtxt can read data only from a file with one column. Is it True or False? 2. Given a file data.txt with three columns of data separated by spaces. Read it into 3 separate simple sequences. |
| 07:58 | 3. Given a file data.txt with three columns of data separated by colon. Read it into 3 separate simple sequences. |
| 08:09 | Now, let us look at the answers. The answer to the first question is False. |
| 08:17 | The loadtxt() command can read data from files having single columns as well as multiple columns. |
| 08:25 | The answer to the second question is-
To separate data into three columns, we use the loadtxt() command as follows: |
| 08:35 | x(equal to)loadtxt(within parentheses and within double quotes)data(dot)txt(after double quotes comma)unpack(equal to)True. |
| 08:50 | The answer to the third question is-
We read into three separate sequences by using an additional argument of delimiter in the loadtxt command. |
| 09:03 | So, x(equal to)loadtxt( within parentheses, within double quotes)data(dot)txt(after double quotes comma)unpack(equal to)True(comma)delimiter(equal to)(within double quotes)colon. |
| 09:22 | Do you have questions on THIS Spoken Tutorial?. Please visit this site. |
| 09:29 | Do you have any general / technical questions? Please visit the forum given in the link. |
| 09:37 | The FOSSEE team coordinates coding of solved examples of popular books. |
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| 09:52 | The Spoken Tutorial project is funded by NMEICT, MHRD, Govt. of India. |
| 09:59 | This is Prathamesh Salunke from IIT Bombay, signing off. Thanks for watching. |
