How does R do it, and should I ever be worried? I always remove
columns by index, and it works exactly as I would naively expect - but
HOW? The second illustration, which deletes non contiguous columns,
represents what I do all the time and have some trepidation about
because I don't know the mechanics (e.g. why doesn't the column
formerly-known-as-4 become 3 after column 1 is dropped: doesn't vector
removal from a df/list invoke a loop in C?). Can I delete a named
list of columns, which are examples 4 and 5 and which generate the
"unary error' mesages, without resorting to "orig.df$num1.10 <- NULL"?
Thanks!
orig.df <- data.frame(cbind(
1:10
,11:20
,letters[1:10]
,letters[11:20]
,LETTERS[1:10]
,LETTERS[11:20]
))
names(orig.df) <- c(
'num1.10'
,'num11.20'
,'lc1.10'
,'lc11.20'
,'uc1.10'
,'uc11.20'
)
# Illustration 1: contiguous columns at beginning of data frame
head(orig.df[,-c(1:3)])
# Illustration 2: non-contiguous columns
head(orig.df[,-c(1,3,5)])
# Illustration 3: contiguous columns at end of data frame
head(orig.df[,-c(4:6)]) ## as expected
# Illustrations 4-5: unary errors
head(orig.df[,-c(as.list('num1.10', 'lc1.10', 'uc1.10'))])
head(orig.df[,-c('num1.10', 'lc1.10', 'uc1.10')])
Mike
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