pkensche at cmbi.ru.nl
2007-Nov-28 08:25 UTC
[Rd] hash access to data.frame uses prefix? (PR#10474)
Full_Name: Philip Kensche Version: R version 2.5.0 (2007-04-23) OS: Linux Submission from: (NULL) (131.174.146.31) I want to access a row of a data.frame() by using the row names as hash keys. This works fine for most keys. Now consider the following data.frame().> x <- data.frame(v=c(V40="a", V411="b"))> xv V40 a V411 b If I query for "V41", which does not exist in the data.frame() the call does not return NA as I would expect but the row "V411".> x[ "V41", ][1] b Levels: a b If there the prefix is not unique the query does not return a results, i.e.> x <- data.frame(v=c(V412="a", V411="b"))> xv V412 a V411 b> x[ "V41", ][1] <NA> Levels: a b sessionInfo() output:> sessionInfo()R version 2.5.0 (2007-04-23) i686-pc-linux-gnu locale: LC_CTYPE=en_US;LC_NUMERIC=C;LC_TIME=en_US;LC_COLLATE=en_US;LC_MONETARY=en_US;LC_MESSAGES=en_US;LC_PAPER=en_US;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US;LC_IDENTIFICATION=C attached base packages: [1] "stats" "graphics" "grDevices" "utils" "datasets" "methods" [7] "base" other attached packages: lattice "0.15-4"
ripley at stats.ox.ac.uk
2007-Nov-28 09:40 UTC
[Rd] hash access to data.frame uses prefix? (PR#10474)
Exact matching has preference over partial matching: see ?pmatch. Your version of R is three versions obsolete: the latest version explains this in detail under ?`[.data.frame` and ?`[` (and maybe 2.5.0 does too). Please do your homework before sending non-bugs to R-bugs. On Wed, 28 Nov 2007, pkensche at cmbi.ru.nl wrote:> Full_Name: Philip Kensche > Version: R version 2.5.0 (2007-04-23) > OS: Linux > Submission from: (NULL) (131.174.146.31) > > > I want to access a row of a data.frame() by using the row names as hash keys.Hmm, you mean you use character vector indices. No hashing is involved.> This works fine for most keys. > > Now consider the following data.frame(). > >> x <- data.frame(v=c(V40="a", V411="b")) > >> x > v > V40 a > V411 b > > If I query for "V41", which does not exist in the data.frame() the call > does not return NA as I would expect but the row "V411". > >> x[ "V41", ] > [1] b > Levels: a b > > If there the prefix is not unique the query does not return a results, i.e. > >> x <- data.frame(v=c(V412="a", V411="b")) > >> x > v > V412 a > V411 b > >> x[ "V41", ] > [1] <NA> > Levels: a b > > > sessionInfo() output: >> sessionInfo() > R version 2.5.0 (2007-04-23) > i686-pc-linux-gnu > > locale: > LC_CTYPE=en_US;LC_NUMERIC=C;LC_TIME=en_US;LC_COLLATE=en_US;LC_MONETARY=en_US;LC_MESSAGES=en_US;LC_PAPER=en_US;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US;LC_IDENTIFICATION=C > > attached base packages: > [1] "stats" "graphics" "grDevices" "utils" "datasets" "methods" > [7] "base" > > other attached packages: > lattice > "0.15-4" > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel >-- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
ripley at stats.ox.ac.uk
2007-Nov-28 09:50 UTC
[Rd] hash access to data.frame uses prefix? (PR#10474)
If you do want only exact matching, use match(). E.g. in your example
x[match("V41", row.names(x)), ]
will give NA as you expected for a construction documented to do something
else.
On Wed, 28 Nov 2007, Prof Brian Ripley wrote:
> Exact matching has preference over partial matching: see ?pmatch.
>
> Your version of R is three versions obsolete: the latest version explains
> this in detail under ?`[.data.frame` and ?`[` (and maybe 2.5.0 does too).
>
> Please do your homework before sending non-bugs to R-bugs.
>
>
> On Wed, 28 Nov 2007, pkensche at cmbi.ru.nl wrote:
>
>> Full_Name: Philip Kensche
>> Version: R version 2.5.0 (2007-04-23)
>> OS: Linux
>> Submission from: (NULL) (131.174.146.31)
>>
>>
>> I want to access a row of a data.frame() by using the row names as hash
>> keys.
>
> Hmm, you mean you use character vector indices. No hashing is involved.
>
>> This works fine for most keys.
>>
>> Now consider the following data.frame().
>>
>>> x <- data.frame(v=c(V40="a", V411="b"))
>>
>>> x
>> v
>> V40 a
>> V411 b
>>
>> If I query for "V41", which does not exist in the
data.frame() the call
>> does not return NA as I would expect but the row "V411".
>>
>>> x[ "V41", ]
>> [1] b
>> Levels: a b
>>
>> If there the prefix is not unique the query does not return a results,
i.e.
>>
>>> x <- data.frame(v=c(V412="a", V411="b"))
>>
>>> x
>> v
>> V412 a
>> V411 b
>>
>>> x[ "V41", ]
>> [1] <NA>
>> Levels: a b
>>
>>
>> sessionInfo() output:
>>> sessionInfo()
>> R version 2.5.0 (2007-04-23)
>> i686-pc-linux-gnu
>>
>> locale:
>>
LC_CTYPE=en_US;LC_NUMERIC=C;LC_TIME=en_US;LC_COLLATE=en_US;LC_MONETARY=en_US;LC_MESSAGES=en_US;LC_PAPER=en_US;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US;LC_IDENTIFICATION=C
>>
>> attached base packages:
>> [1] "stats" "graphics" "grDevices"
"utils" "datasets" "methods"
>> [7] "base"
>>
>> other attached packages:
>> lattice
>> "0.15-4"
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
>
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595