Preface to First Edition - lib

BASIC DATA MANIPULATION 11The function odbcConnectExcel opens a connection to the specified Excel orAccess file which can be used to send SQL queries to the data base engine andretrieve the results of the query.Files in SPSS format are read in a way similar to reading comma separatedfiles, using the function read.spss from package foreign (which comes withthe base distribution).Exporting data from R is now rather straightforward. A comma separatedfile readable by Excel can be constructed from a data.frame object viaR> write.table(Forbes2000, file = "Forbes2000.csv", sep = ",",+ col.names = NA)The function write.csv is one alternative and the functionality implementedin the RODBC package can be used to write data directly into Excel spreadsheetsas well.Alternatively, when data should be saved for later processing in R only, Robjects of arbitrary kind can be stored into an external binary file viaR> save(Forbes2000, file = "Forbes2000.rda")where the extension .rda is standard. We can get the file names of all fileswith extension .rda from the working directoryR> list.files(pattern = "\\.rda")[1] "Forbes2000.rda"and we can load the contents of the file into R byR> load("Forbes2000.rda")1.6 Basic Data ManipulationThe examples shown in the previous section have illustrated the importance ofdata.frames for storing and handling tabular data in R. Internally, a data.frameis a list of vectors of a common length n, the number of rows of the table. Eachof those vectors represents the measurements of one variable and we have seenthat we can access such a variable by its name, for example the names of thecompaniesR> companies companies[1][1] "Citigroup"and the top three companies can be extracted utilising an integer vector ofthe numbers one to three:R> 1:3© 2010 by Taylor and Francis Group, LLC