Reading and writing CSV files

In the previous recipe, we downloaded the historical S&P 500 market index from Yahoo Finance. We can now read the data into an R session for further examination and manipulation. In this recipe, we demonstrate how to read a file with an R function.

Getting ready

In this recipe, you need to have followed the previous recipe by downloading the S&P 500 market index text file to the current directory.

How to do it…

Please perform the following steps to read text data from the CSV file.

1. First, determine the current directory with getwd, and use list.files to check where the file is, as follows:

   > getwd()
   > list.files('./')
   

2. You can then use the read.table function to read data by specifying the comma as the separator:

   > stock_data <- read.table('snp500.csv', sep=',' , header=TRUE)
   

3. Next, filter data by selecting the first six rows with column Date, Open, High, Low, and Close:

   > subset_data <- stock_data[1:6, c...