How do you represent a 3x3 matrix in R?

Matrix (matrices) is a data type in R used in many mathematical problems. A matrix has rows and columns. A 3 by 3 matrix has 3 rows and 3 columns. A matrix can have only columns, only rows and both columns and rows.

Here is an example of a 3x 3 matrix.

1, 2, 3
4, 5, 6
7, 8, 9

Let us create a matrix which is obtained by arranging the data, a vector of values 1,2,3,4,5,6,7,8,9 by assigning three elements each to a row and create 3 columns from the rows. This is how you do it in R.

Matrix_1

If you want to find the elements of this matrix, you provide the row and column where your element is found as shown.

You find 5 in the 2nd row and 2nd column and you find 6 in 2nd row and 3rd column.

Matrix_2
How do you arrange the same vectors column-wise arranged. You use the same definition as in the previous but omit, byrow attribute as shown.

Matrix_3

This is just the basic but you can do a whole lot more using R.

How does TableSample in FROM clause of a SELECT Query work?

TableSample clause started with SQL Server 2015 limits the number of rows returned from a table to a sample % or sample numbers. In fact, it may not provide the specified rows of %. Also, it is not for tables with too few rows.

Here is how TableSample is defined in the MSDN site:

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TABLESAMPLE (10 PERCENT) /*Return a sample 10 percent of the rows of the result set. */
TABLESAMPLE (15 ROWS) /* Return a sample of 15 rows from the result set. */.

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For these scenarios it cannot be applied:

Derived tables
Linked Server Tables
Tables from Table-Valued functions
Row-set functions
Open XML

This here is the syntax for TableSample clause:

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TABLESAMPLE [SYSTEM] (sample_number [ PERCENT | ROWS ] )

[ REPEATABLE (repeat_seed) ]

TableSample in FROM Clause does not behave as defined in the syntax and could provide surprising results:

I queried the Northwind databases Orders table using the following syntax in SQL Server 2016 Developers edition.

SELECT * FROM Orders TableSample(10 Percent)

SELECT * FROM Orders TableSample (10)--surprisingly this does not result in error

SELECT * FROM Orders TableSample (10 ROWS)

These queries were run a number of times and the rows returned were variable from run to run and some times resulted in 0 returned rows.

More details here:
https://hodentekmsss.blogspot.com/2018/03/tablesample-in-from-clause-to-limit.html