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# Section 4
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# Find out which packages are loaded:

search()

# information on available built-in datasets:

help(package=datasets)

# list what is currently in the workspace:

ls()

# load some datasets:

data(state)

data(mtcars)

ls()

search()

objects(3)  # list the elements in the third object in search path

mtcars

mpg

mtcars$mpg

# attaching data frames:

attach(mtcars)

mpg

detach(mtcars)

rm(mtcars, state.area, state.division, state.center)

# do ls, search, objects to find mtcars

search()

objects(1)

# More examples:

#Load monarchs.dfr and trees
data(trees)
attach(trees)
ls()
objects(2)

#Attaching dataframes
Mname.cvec=as.character(Mname)
monarchs.dfr=data.frame(Mgroup,I(Mname.cvec),yrslived)
monarchs.dfr

rm(Mgroup,Mname.cvec,yrslived)
attach(monarchs.dfr)
search()
detach(monarchs.dfr)
yrslived
attach(monarchs.dfr)
yrslived
attach(monarchs.dfr,pos=3)  

# note the warning message when you attach a data frame that is already attached

search()


#Data directory maintenance
rm(monarchs.dfr,trees)