Matrices can be subsetted, in the kind of the, the way that you would expect.

So the first index is going to be, the, the row index, the second index is

going to be the column index, and we can use numbers for this too.

So, so for example, x is a matrix, it's a two by three matrix with the numbers one

through six in it, if I take x with the, with the [1, 2] that gives me

the first row second column, and so that's going to be the, the number three, and

then the, the second row first column is going to be the number two.

You don't have to always specify both indices when subsetting a matrix, So for

example if I say x bracket 1, comma and then blank for the second index,

that's in, that notation indicates that I want the first row of the matrix,

in which case the, this is a vector one, three, five.

If I wanted the second column of the matrix I could just leave the first index

blank and say x bracket and

then comma two, that gives me the second column which is three, four.

So by default when a single element of a matrix is retrieved,

is returned to vector of length one, rather than a one by one matrix.

So remember I said that before, the si, the single square operator always

returns an object of the same class, so, the one that's, that sometimes is

a little bit unexpected, is that if I subset out, a single element of a matrix,

I don't get back a matrix, what I get back is just a vector with that number in it,

so if I say x, one, two, that gives the first row second column of the matrix,

that's just a number three, and what I get back is a number three,

[COUGH] not a one by one matrix, with the number three in it.

This is usually what you want, although sometimes it can cause problems, and so

you can turn off this default behavior by adding an extra argument to

the subsetting operation, which is called drop.

And the idea is that by default, drop is equal to true, and

it drops the dimension, and so rather than getting a two dimensional object back,

you, you typically get a one dimensional object back.

However if you want to preserve the dimensions of the object,

you can say drop equal to false and when I subset out the first row,

second column, what I get back is a one by one matrix with the element three in it.

Now also when you subset a single column or

a single row, you don't, you, you by default, you don't get a matrix back, so

for example, if I subset out the first row here you might think that, well,

what should be returned, is really a one by three matrix where there's one row and

three columns, and the elements are one, three, five.

Well that's not actually what you get back,

what you get back, is a vector with the elements one, three, five.

Usually this is what you want, and it's okay, but if it's not, then you can

always set the drop equal to false argument when you subset the matrix, and

then you get a one by three matrix with the elements one, three, and five in it.

Subsetting - Matrices