Right is this data, you know this picture or that data

Is this data? What what is data?

So we talked a lot about data in the last video

Why is it important that we can analyze and understand data, but what is data? Everybody has data everybody's generating it

Companies are generating on us. We're generating it ourselves, you know when we use social media so on

but what is it and

Understanding what it is is a prerequisite for being able to use it properly

Perhaps the most important thing as far as we're concerned

So people who are trying to analyze data sort of scientifically is the data has to be measurable, right?

so the idea is, you know, if you're going to do a survey on what people like

Everyone's got to be using the same scale and the same rating system

Otherwise, it doesn't make any sense

Well, we can't have someone rating things from one to five and someone else saying I thought it was good

Right because which one of one to five is good. We don't you know, we don't know

All right

So everyone is going to be doing the same thing your data's got to be a consistent format and once that's achieved at least

We're a little bit closer

To be able to make some sense of it. Broadly speaking when we talk about data

We kind of have four different types and we summarize this with this nice noir word. So n, o, i, r, noir

And each of these different types of data we can do different things with all right

So n that's the first type so this is nominal data

The normal data is where we have no distance between the values that we can measure

Right because they're not really quantities and we can't order them. So a good example would be colors

So maybe you have your favorite color is red. And my favorite color is blue

I don't know which is better than the other

There is no measurement between them right is blue closer to green the medes. You know, that doesn't make any sense, right?

We're not talking about wavelengths. We're just talking about the colors, right?

Another good example would be lets say in football player numbers on your back right now symbolically

Sometimes certain player numbers have a meaning but you can't compare and contrast them

You can't say that 8 is 2 times better than 4. All right, that doesn't make any sense, right?

You also can't really order them in general right player

16 doesn't go before or after player 13 in a list but you know, but that doesn't make any sense, right?

So nominal data is data where and it's useful, right?

It could be really important but it's data where we we kind of have labels

But no way of ordering these labels so you can still analyze it, but you can't for example calculate

the average that the mean average right? That wouldn't make any sense

What you can do is calculate the mode so you can calculate the most common one so you could say that more people prefer red

To blue but you couldn't say you know

The average color that people like is a sort of muddy brown right. That doesn't make any sense at all, right

So as we go down this list, we get slightly more and more informative in some sense types of data

So the next one is ordinal

so in ordinal data

we have an order but we can't measure distances between things so a good example would be something like

Positions people finished in a race. So, you know, maybe I finished first

I'm super quick right you didn't you finished third

But how far we are a part that isn't included in that kind of data

You'd have to have a separate value for that another example what we're all familiar with is rating systems, right?

So perhaps you I rate a film from one to five stars and you rate the film from one to five stars

but you can't really say that a

film that's got four stars is two times better than one that scored two

Because that's a very subjective and it's there's no real sort of measurable distance between these stars if you have ordinal data

You can calculate the mode again. You can calculate the most

Common value of all the values that were returned or you can calculate the median the one that sits in the middle, right?

So maybe you know fifty runners in a race the 25th position roughly speaking is going to be you know around the median

So it's still not hugely useful, right the next up. We have interval data interval data

We have an order and we have a distance, but we have no sort of absolute zero for this scale

So a good example would be something like degree Celsius or degrees Fahrenheit

Zero degrees Celsius isn't no temperature. It's it's a specific temperature, right?

So we can't say that fifty degrees is half of a hundred degrees

I have a numbers a half but doesn't really make sense, right?

They are we can we can say that a hundred degrees is hotter than 50, which is hotter than zero, right?

So this is interval data now interval data

Lets us do a few more things than we could with ordinal as well as be able to calculate the mode and median we can

Now calculate the mean temperature. That's okay

And we could also calculate things like the rain the minimum and maximum temperatures for a certain window, right?

So that's pretty useful another good example of interval will be pH level right again, the pH of zero means very acidic

It doesn't mean there is no acidity at all or no pH at all. We can say that a

So 13 is higher than a pH of 7 is higher than a pH of 3

And we know how far apart these numbers are but we can't necessarily say if one is double one another one

So the final kind of data we're going to look at is ratio data

So this is exactly like interval, except we now have a sort of true zero value

So a good example of this would be degrees Kelvin right. So Kelvin has an absolute zero which is the absolute average

absence of any kind of heat right and when it goes upwards so we can say that in terms of Kelvin a hundred is

Half of 200 and so on like this and we can get to 0 another example would be number of children, right?

Zero children means the absence of any children and you can also say that let's say four children is double the amount of two children

And two many to look after in my opinion

So that is an example of ratio data

Right now ratio data is quite similar in terms of what you can calculate to interval, but it allows some more

complicated statistical measures such as t-test

So these are the types of data now actually, it's quite important how you structure your data in general

We can't just have it sitting in some massive spreadsheet with no thought given to where everything is, right

There's actually a pretty standard way of doing this that we're going to look at

Data comes in lots of forms, right different types of measurements different experiments people are going to collect it in different ways

But actually there's a very standard way that we use

To represent data once it's actually on a computer so we can have some kind of table of our data

We almost always

represent our data in a matrix like this a

Two-dimensional table because it's much easier to do and so along the top

We're going to have our attributes right which are the the things we've been measuring

So an example would be maybe we're collecting data on people so we could have name

That would be some nominal data and then, you know age height

So the columns are attributes all the things we've been measuring the rows

Those are the instances or the samples we've got so that's all the individual people

So here's person 1 and person 2 person 3 and person 3 is called John and there

You know 54 and you know 5 foot 11 or whatever, you know

Whatever right and so on and you can put you know have as many rows as you want

so when we talk about

attributes

We're talking about the number of columns people use lots of different terms for these. I like to think of them as features

Attributes is another one and we have instances or samples down the rows now quite often on the very last column of your data

Sometimes separated out but not really important. We'll have our output

Maybe we're trying to make a decision based on these people

Maybe these are candidates for a football team and we're saying, you know, are they gonna be on the team or not?

So this is yes. No John's made it

Yes, no, no and so on and that way we could perhaps analyze our decision-making process and decide you know

Is there any aspect of these things that inform our decision-making process as an example right now?

We always structure data in this way

But if we don't it becomes a huge problem because you end up spending all this time formatting and trying to work out

What's what and you know, why is John listed down the table or not across the table? And you know, nothing makes any sense anymore

So let's look at an actual data set and we'll see all this in action

So we have here a data set of whether someone goes to play tennis

Right and whether or not they go is going to depend a little bit on what the weather conditions are, right

So we don't like to play for example

When it's too hot the tennis data set is just the same structure as a data set. We looked at already

We're gonna load it into R it's held in a CSV file. So tennis read CSV

Tennis now we're using R for this because it's free and it has a load of decent functions for analyzing examining

Visualizing data, right? So we're going to be using it throughout these videos

obviously you could use MATLAB or Python or some other library if you wanted to

I think that you should use whatever you're most comfortable with

Looking at these rows and tables

I mean, it looks a lot like something like Microsoft Excel

You could do this data analysis in Excel

Some people would disagree. No, Excel is perfectly good for what it does you could do with data analysis in it. I think that

Excel in it doesn't enforce anything to do with

Observations versus variables and things like that. These are distinctions that are not really made in Excel

Obviously if you enforce those rules yourself that's going to work, but you have to be a little bit more

You know regimented and rule-based about it

Think the consensus would be that if you really want to get into data analysis and start doing things like principal component analysis or more

Advanced statistical measures something like R or Python is going to help a lot more

Okay

So I've loaded the data set and if we look up the data set

so we look at the top few rows of the data you'll see that there are 6 different variables or 6 attributes and

This data set has 14 instances or observations

R calls them observations. So what we're saying is we have six columns and

fourteen rows right of our data set and this data set is

structured exactly like

This people data set that I was looking at a minute ago

So we can examine a single instance we can say what is it about day three?

So let's have a look at day three so we can say tennis on day 3

And we can say on day three it was overcast. The temperature was only five degrees

The humidity was high there wasn't any wind so they decided to play tennis, right?

So it's a bit chilly, but I guess they gave it a go

So on we could also look at all the different temperatures, for example, all the different forecasts tennis dollar outlook

All right

And we can look at all the outlooks in the data set so we can say we've got sunny sunny overcast rainy rainy

rainy and so on and we can get a feel for what kind of weather we're looking at here as well using something like R

You can examine the instances

You can examine the individual attributes you can group them together or not as you see fit and then you can start to drill into

What this dataset means

Now this dataset has in it the final column which is whether they actually played so you could use something like machine learning

To predict that final column based on the other columns. That's something you could do one other thing about this dataset

It's quite interesting is it has a few examples of the different kinds of data. We were looking at earlier

So remember we have nominal ordinal interval and ratio

So for example Outlook is really a nominal field right, it's a nominal data type

You could perhaps suggest that you could order it from rainy through to sunny, but then cloudy overcast, you know

It doesn't really make any sense

so this is kind of nominal you could calculate for example the mode and say that most of the days were rainy or something like this