# NOT RUN {
# Type 'example(copy)' to run these at prompt and browse output
DT = data.table(A=5:1,B=letters[5:1])
DT2 = copy(DT) # explicit copy() needed to copy a data.table
setkey(DT2,B) # now just changes DT2
identical(DT,DT2) # FALSE. DT and DT2 are now different tables
DT = data.table(A=5:1, B=letters[5:1])
nm1 = names(DT)
nm2 = copy(names(DT))
DT[, C := 1L]
identical(nm1, names(DT)) # TRUE, nm1 is also changed by reference
identical(nm2, names(DT)) # FALSE, nm2 is a copy, different from names(DT)
# }
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