Reading .csv files into RStudio

Hi. In this video, I'm going to
show you how you can read

in, .csv files, data files into R

so that you can do your data analysis.

The first thing you need to do
is to set your working directory.

That is something that was described
and talked about in a previous video.

So navigate to the folder of wherever

the data set you want
to bring into R is located.

And I have already done so because
the data set I want to bring into

R is called MRI.csv.

Okay.

So if I want to bring in a CSV file-

Uh, CSV stands for Comma Separated Values.

Usually, it is opened up
in a program like Excel.

If I want to bring this data file into R,

I will use the read.csv function.

And inside

the parentheses I will put
the name of the data.

And R is case sensitive.

So you need to make sure
you spell it exactly how it is

saved as. Underscores, spaces, anything.

And then you always need
to include the file extension,

which is .csv.

Okay.

Let's go ahead and run this
and see what happens.

This is also really nice and looks good.

So it looks like it read
in our data just fine.

And it saw here,

"Oh look these are column titles."

So this is, if you saw the .txt video
that I did previously, this is something

that's different between the read.csv
function and the read.table function.

If your data-

notice like, what if I did
something like oh, sorry.

Wrong spot.

If I said this

command, I'll explain what
this means in a second.

Notice what R does.

It interprets

this very first line of code to be

an observation rather than-
though not this very first line.

And interprets the first line of the
data to be an observation of data,

when in fact it really is

the titles of your columns or the
names of all of your variables.

Read.csv is smart and
knows that most likely

your data is going to have
what we call a header.

But if your data happens
to not have a header-

So pretend that this first line
was actually data, but you wanted to

still be able to refer to the columns
as column one, two, three, four.

You could say header equals false,
meaning I don't have a header.

So please assign them
one, two, three, four, etc.

If you do have a header,

in our case we do

make sure to type out
header equals true.

And notice what happens is that

R is able to notice that

the first line of your data
was the column titles.

And that is to not treat it
as an observation of data.

Good practice is to always
include this header argument,

and say header equals true
or false no matter what.

Notice also that I
had to do in all caps.

If I try and just do capital T

or thinks I'm writing
just like the word true,

and it's not actually meaning internally,
like a logical value called true.

So I need to have it in all caps.

You can also do just the letter T

or just the letter
F for true and false,

but it's better practice
to write out the entire word.

Okay, so this is nice that

you can bring in your CSV file into R,

but in order to do much of anything
with it, we need to kind of,

we need to save it into our R environment

so that we can do
further analysis with it.

So rather than just running
just this read.csv line,

in front of it, put, give this data,

set a name that you, that you can
call it, call it whatever you want.

I'm going to call it MRI data.

And then in between the
name and this command,

you're going to put in what we
call the assignment operator.

And it is a less than sign and a dash.

What this means is this little
piece of code right here.

Read.csv header equals true.

What that did is it brought
that data and said here it is.

But it didn't actually
do anything with it.

So what it's going to do is it's
going to take this data and store it.

And it kind of looks like it's like
pushing, the arrow is pushing into here.

It's going to take this data and store it
in a little box called MRI data.

If we run this line of code

notice what happens over here
in our global environment.

It now shows 'hey,

you have now stored a data
set here in R called MRI data.

There's 15 observations and
11 variables,' which is true.

We have 15 observations and 11 variables.

And now you should
be able to do, use,

you can just refer to the data by whatever
name you called it which is MRI data.

And R will always know,
hey, that's the data set

I'm supposed to
be using whenever,

you type MRI data.

So that is how you can read in

.csv files into R

and how you can then save
it into your environment

so that you can do further,
data analysis work with it.

Don't forget to set your working
directory at the very beginning,

and then remember that
R is case sensitive.

And to not forget
the header argument.

And that should be
everything that you need.

Good luck and have fun in R.