Exercise

# Creating tables with big.matrix objects

A final advantage to using `big.matrix`

is that if you know how to use R's matrices, then you know how to use a big.matrix. You can subset columns and rows just as you would a regular matrix, using a numeric or character vector and the object returned is an R `matrix`

. Likewise, assignments are the same as with R matrices and after those assignments are made they are stored on disk and can be used in the current and future R sessions.

One thing to remember is that `$`

is not valid for getting a column of either a `matrix`

or a `big.matrix`

.

Instructions

**100 XP**

- Create a new variable
`mort`

by attaching the`"mortgage-sample.desc"`

file. - Look at the first 3 rows of
`mort`

. - Create a table of the number of mortgages for each year in the data set. The column name in the data set is
`"year"`

.