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.

This exercise is part of the course

Scalable Data Processing in R

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Exercise instructions

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".

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

# Create mort
mort <- ___

# Look at the first 3 rows
mort[___, ]

# Create a table of the number of mortgages for each year in the data set
table(___)

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