Reading chunks in as a matrix
In this exercise, you'll write a scalable table() function counting the number of urban and rural borrowers in the mortgage dataset using chunk.apply(). By default, chunk.apply() aggregates the processed data using the rbind() function. This means that you can create a table from each of the chunks and then add up the rows of the resulting matrix to get the total counts for the table.
We have created a file connection fc to the "mortgage-sample.csv" file and read in the first line to get rid of the header.
This exercise is part of the course
Scalable Data Processing in R
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Define the function to apply to each chunk
make_table <- function(chunk) {
# Read each chunk as a matrix
x <- ___(chunk, type = "integer", sep = ",")
# Create a table of the number of borrowers (column 3) for each chunk
table(x[, 3])
}