WEBVTT

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Welcome back.

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Let's say you have a log file that contains information about the Web site visits.

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In this lecture you're going to learn how to analyze or in other words how to parse a log file and generate

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a report first of all let me show you how the program is going to work.

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This is the log file.

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You can find it from the resources of this lecture.

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As you can see there are two fields per line separated by a space character.

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The first field is the domain name and the second field is the number of visits for that domain in the

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log file.

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The domains are duplicated.

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So you need to aggregate them to print the total visits per domain.

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Let me run the program by redirecting its standard input to the file like so as you can see it passes

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the file and it prints the total visits per domain.

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All right let's get started.

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First of all let me create a new scanner that uses the standard input.

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Let's scan the log file line by line by calling the scan method there are two fields per line.

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So now I'm going to split them.

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Remember the text method returns the current line and the fields function splits the line into the words.

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Now the fields variable contains a string slice. Let me print them so you can see how it works.

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I'm going to say.

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Domain dash visits I'm going to give it fields 0 and fields 1 the program correctly parses the log

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file to make the code easier to read.

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I'm going to put the fields in variables first.

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Let's declare a variable for the domain name.

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Let's convert the visits field to an integer.

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For now I've skipped the error handling.

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I'll do that later.

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You need to keep of the total total visits per domain.

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So I'm going to create a map variable like so it will store the domain names and the total visits per

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domain.

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I also need to initialize the map okay.

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Now it's time to calculate the total visits for the domains.

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First I'm going to get the total visits from the map and I'm going to add the current visits to the

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map.

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So if the domain name doesn't exist the map will create a new key for the domain and it will set it to

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the visits variable.

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Otherwise it will only increase the total visits for the domain.

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Okay.

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Now it's time to print the map first.

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Let's print the header for the domain names and total visits next.

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Let's draw a horizontal line forty five

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characters are fine.

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Now I'm going to range over the map.

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Like so

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and I'm going to print the total visits per domain it works.

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So it brings the total visits per domain.

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However when I run it a few times as you can see it prints the domain names randomly.

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As I explained in the last lecture before usually, you shouldn't loop over the maps.

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It's a tell-tale sign of a design mistake.

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So what should you do.

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I'm going to go to the top of the file here.

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I'm going to declare a slice to store the unique domain names instead of using the map for printing

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the domain names.

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I'm going to use this slice.

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Okay let's go down here.

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I'm going to check whether the domain is in the map or not.

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Like so the domain doesn't exist in the map.

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I'm going to add it to the slice.

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This way the slice will only contain the unique domain names here.

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Instead of looping over the map I'm going to loop over the domain slice instead I so for the total visits

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I'm going to get it from the map instead like so

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even though I run it several times it always prints the result in the same order.

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Awesome. Let's also sort the domain names using the sort package like so cool.

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Okay.

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Let me also print the total visits for every domain.

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To do that let's go to the top of the file here.

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I'm going to declare a variable like so.

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Now let's go down to the loop here.

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I'm going to add visits and total visits OK.

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Let's go down and let's printed here

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also.

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Now it's time to handle the errors.

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Let's go to the beginning of the loop.

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First I'm going to check whether the current line has two fields or not.

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If not I'm going to say wrong inputs like so

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OK let's test it.

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To do that I'm going to duplicate the log file here I'm going to remove the second field here to check

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whether I correctly handled the error or not like so. Let me say this file as log_err_missing.txt.

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whether I correctly handled the error or not like so. Let me say this file as log_err_missing.txt.

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Let's try it with the incorrect log file first.

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Cool the program detects the error okay.

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Now let's try something else.

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Let me duplicate the log file again.

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Let me change the value of the visits to a string this time I'm going to save it as log_err_str

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the program skips that line.

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So it ignores the error.

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This is not good.

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Let's handle the error like so. If there is an error I'm going to say wrong input then I'm going to

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terminate the program. Cool, it detects the error but not so fast.

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Let's see what happens if there is a negative visits count.

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Let me duplicate log file again.

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Here I'm going to change this to a negative number.

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This time I'm going to save it as log_err_negative. Visits to a domain should always be zero or

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a positive number.

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Right.

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So let's see what happens.

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It says minus forty four people have visited all the domains.

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Clearly I should handle this error as well.

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To do that I'm going to add another condition here like so call it works.

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Let's make the error message more descriptive by adding the error line as well.

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To do that let's go to the top here.

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I'm going to declare a new variable lines.

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Now let's go to the loop here.

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I'm going to increment it.

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OK let's add it to the error messages.

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First I'm going to print the error line for the first message.

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Like so

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Cool, now it tells you that the error is in the third line.

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So, why stop here?

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Let's also add it to the second error message as well like so

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excellent.

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It works.

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OK now let's handle the error from the scanner as well.

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Let me also print it.

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All right.

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That's all for now in the upcoming sections you will revisit this project several times.

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So, well done, congrats!

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See you in the next section.