e-book
"Practical Data Cleaning: 19 Essential Tips to Scrub Your Dirty Data"
by Lee Baker (Ph.D.)
http://channels.theinnovationenterprise.com/ebooks/practical-data-cleaning
Importing data from Excel
StatSoft blog example
Importing data from .csv, .txt, .rtf, or tab-delimited file
Importing data from MS Access using ODBC
Stacking and unstacking data (in R, 'wide' to 'long' format)
Using Visual Basic for Applications (VBA) in MS Excel to reformat data
Recoding variables
Creating a subset of a data file
Joins (inner, outer; left, right)
Merge
sqldf home page http://sqldf.googlecode.com