Dave Mason continues his look at matrices in R:

We can extract an entire row from a matrix. To do this, specify the desired row only within the square brackets [ ]. The placeholder where you would otherwise specify the column is left empty.

> #Points scored by Kendrick Perkins. > points_scored_by_quarter[1,] 1st 2nd 3rd 4th 2 2 6 0 > points_scored_by_quarter["Perkins",] 1st 2nd 3rd 4th 2 2 6 0Conversely, we can extract a column from a matrix. Specify the column within the square brackets [ ]and omit the row. The result is a vector, thus the pivot effect–the row names are displayed in the output (not the column name).

Dave points out that working with matrices is basically an extension of working with vectors.