On 2010-08-05 12:14, Ulrike Grömping wrote:
Gabor Grothendieck schrieb:
On Thu, Aug 5, 2010 at 12:24 PM, Ulrike Grömping
<groemp...@bht-berlin.de> wrote:
Dear developeRs,
I have just discovered a strange feature when assigning some values to
columns of a data frame: The column is matched by partial matching (as
documented), but when assigning a value, a new column with the partial name
is added to the data frame that is identical to the original column except
for the changed value. Is that intentional ? An example:
Note that the lack of partial matching when performing assignment is
also documented.
See second last paragraph in Details section of ?Extract
Yes, I see, thanks. I looked at ?"[.data.frame", where this is not
documented.
However, given the documentation that partial matching is not used on
the left-hand side, I would have expected even more that the assignment
sw$Fert[1]<- 10
works differently, because I am using it on the left-hand side.
Probably, extraction ([1]) is done first here, so that the right-hand
side won. At least, this is very confusing.
Best, Ulrike
This is another example of why it's a good idea to avoid
the '$' notation when fiddling with data frames. Try this:
sw <- swiss[1:5, 1:4]
sw[["Fert"]]
sw[["Fert"]] <- 10
and my preferred version:
sw[, "Fert"]
sw[, "Fert"] <- 10
I've never liked partial matching for data frames.
-Peter Ehlers
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