Input and output

Question 1

load()

Answer 1

load the datasets written with save

Question 2

data(x)

Answer 2

loads specified data sets

Question 3

library(x)

Answer 3

load add-on packages

Question 4

read.table(file)

Answer 4

reads a file in table format and creates a data
frame from it; the default separator sep=”” is any whitespace; use header=TRUE to read the first line as a header of column names; use as.is=TRUE to prevent character vectors from being converted to fac- tors; use comment.char=”” to prevent “#” from being interpreted as a comment; use skip=n to skip n lines before reading data; see the help for options on row naming, NA treatment, and others

Question 5

read.csv(“filename”,header=TRUE)

Answer 5

id. but with defaults set for reading comma-delimited files

Question 6

read.delim(“filename”,header=TRUE)

Answer 6

id. but with defaults set for reading tab-delimited files

Question 7

read.fwf(file,widths,header=FALSE,sep=””

Answer 7

read a table of f ixed width f ormatted data into a ’data.frame’; widths
is an integer vector, giving the widths of the fixed-width fields

Question 8

save(file,…)

Answer 8

saves the specified objects (…) in the XDR platform-

independent binary format

Question 9

save.image(file)

Answer 9

saves all objects

Question 10

cat(…, file=””, sep=” “)

Answer 10

prints the arguments after coercing to

character; sep is the character separator between arguments

Question 11

print(a, …)

Answer 11

prints its arguments; generic, meaning it can have differ-

ent methods for different objects

Question 12

format(x,…)

Answer 12

format an R object for pretty printing

Question 13

write.table(x,file=”“,row.names=TRUE,col.names=TRUE,

sep=” “)

Answer 13

prints x after converting to a data frame; if quote is TRUE, character or factor columns are surrounded by quotes (“); sep is the field separator; eol is the end-of-line separator; na is the string for missing values; use col.names=NA to add a blank column header to get the column headers aligned correctly for spreadsheet input

Question 14

sink(file)

Answer 14

output to file, until sink()
Most of the I/O functions have a file argument. This can often be a charac- ter string naming a file or a connection. file=”” means the standard input or output. Connections can include files, pipes, zipped files, and R variables. On windows, the file connection can also be used with description = “clipboard”. To read a table copied from Excel, use
x ,col.names=NA)
For database interaction, see packages RODBC, DBI, RMySQL, RPgSQL, and ROracle. See packages XML, hdf5, netCDF for reading other file formats.