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
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(___)