Reading Data in R

Module 3

Reading a File

From a CSV file

read.csv() reads a comma separated file and returns a data frame.

penguins <- read.csv("penguins.csv")
str(penguins)

The str() call prints the structure of the object, so you can check the column types before going further.

From a CSV file

Two arguments matter more than the others.

  • stringsAsFactors controls whether character columns become factors.
  • na.strings lists the values to read as missing.

From an Excel file

R has no built-in reader for Excel files, so you need a package.

readxl::read_excel("penguins.xlsx", sheet = "data")

Common Pitfalls

Separators and decimal marks

Function Separator Decimal mark
read.csv() , .
read.csv2() ; ,
read.delim() tab .

Pick the reader that matches the file you were given, rather than reading the file and repairing it afterwards.

Checking your work

Always print the dimensions of what you read.

dim(penguins)