There are many ways to import data from Excel files. Here we mention two popular ways
1) Export the Excel file to .csv file, e.g., "storeSales.csv", then use R command
x<-read.csv("storeSales.csv",na.strings="N/A");
2) Use the "readxl" package. This is just one of many packages around that import data from Excel sheets, but according to several simulations, it is considerably faster than other packages such as "gdata", "xlsx", "openxlsx", in dealing with large Excel files (e.g., an Excel file with 25000 rows)
install.packages("readxl");
library(readxl);
x<-read_excel("storeSales.xls",na="NA");