On Jan 6, 2012, at 11:43 AM, Mike Harwood wrote:
Thank you, David. I was merely using "head" to limit the code/
output. My question remains, because a created data frame has the
same columns as was output from "head":
head(orig.df,3)
num1.10 num11.20 lc1.10 lc11.20 uc1.10 uc11.20
1 1 11 a k A K
2 2 12 b l B L
3 3 13 c m C M
# Illustration 1: contiguous columns at beginning of data frame
head(orig.df[,-c(1:3)],2)
lc11.20 uc1.10 uc11.20
1 k A K
2 l B L
new.df <- orig.df[,-c(1:3)]
head(new.df,2)
lc11.20 uc1.10 uc11.20
1 k A K
2 l B L
# Illustration 2: non-contiguous columns
head(orig.df[,-c(1,3,5)],2)
num11.20 lc11.20 uc11.20
1 11 k K
2 12 l L
new.df <- orig.df[,-c(1,3,5)]
head(new.df,2)
num11.20 lc11.20 uc11.20
1 11 k K
2 12 l L
I guess my short attention span got the better of me. (But calling
them "unary errors" was somewhat cryptic and not a particularly
helpful description of what you were actually seeing.) Here are more
constructive responses:
Negative indexing is not accepted for character vectors, so you need
to convert to either numeric or logical and then "negativize":
orig.df[ !names(orig.df) %in% c('num1.10', 'lc1.10', 'uc1.10')]
These are equivalent:
orig.df[ , !names(orig.df) %in% c('num1.10', 'lc1.10', 'uc1.10')]
orig.df[,-match( c("num1.10", "lc1.10", "uc1.10"), names(orig.df))]
orig.df[ , -sapply(c('num1.10', 'lc1.10', 'uc1.10'), grep,
x=names(orig.df)) ]
And when there is a pattern, such as with your not wanting any of the .
10" names, then grep can be quite efficient:
orig.df[ , -grep(".10", names(orig.df), fixed=TRUE)]
--
David
On Jan 6, 9:49 am, David Winsemius <dwinsem...@comcast.net> wrote:
On Jan 6, 2012, at 10:00 AM, Mike Harwood wrote:
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?).
You are NOT "removing columns". You are returning (to `head` and then
to `print`) an extract from the dataframe, but that does not change
the original dataframe. To effect a change you would need to assign
the value back to the same name as the original daatframe.
--
David
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
______________________________________________
r-h...@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
r-h...@r-project.org mailing listhttps://stat.ethz.ch/mailman/
listinfo/r-help
PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
