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Column classes

Next to column names, you can also specify the column types or column classes of the resulting data frame. You can do this by setting the colClasses argument to a vector of strings representing classes:

read.delim("my_file.txt", 
           colClasses = c("character",
                          "numeric",
                          "logical"))

This approach can be useful if you have some columns that should be factors and others that should be characters. You don't have to bother with stringsAsFactors anymore; just state for each column what the class should be.

If a column is set to "NULL" in the colClasses vector, this column will be skipped and will not be loaded into the data frame.

This exercise is part of the course

Importing Data in R (Part 1)

View Course

Exercise instructions

  • The read.delim() call from before is already included and creates the hotdogs data frame. Go ahead and display the structure of hotdogs.
  • Edit the second read.delim() call. Assign the correct vector to the colClasses argument. NA should be replaced with a character vector: c("factor", "NULL", "numeric").
  • Display the structure of hotdogs2 and look for the difference.

Hands-on interactive exercise

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

# Previous call to import hotdogs.txt
hotdogs <- read.delim("hotdogs.txt", header = FALSE, col.names = c("type", "calories", "sodium"))

# Display structure of hotdogs


# Edit the colClasses argument to import the data correctly: hotdogs2
hotdogs2 <- read.delim("hotdogs.txt", header = FALSE, 
                       col.names = c("type", "calories", "sodium"),
                       colClasses = NA)


# Display structure of hotdogs2
Edit and Run Code