My question must be a trivial one.
There is automatic coercicion to vector when extracting only one line of a
matrix.
# example
A = matrix(1:12,3,4)
rownames(A) = c('a1','a2','a3')
i = 1:2
A[i,]
# [,1] [,2] [,3] [,4]
# a1 1 4 7 10 matrix
# a2 2 5 8 11
i = 1
A[i,]
# [1] 1 4 7 10 vector !!!
# to get the rowname, it is necessary to do
rownames(A)[i]
# [1] "a1"
Is it possible to get a (1,4)-matrix (without testing length(i) ) ? I see
nothing in options()...
Jean Coursol
>From one Jean to another ... A[i, , drop=FALSE]On Sat, Mar 21, 2015 at 6:04 AM, <Jean.Coursol at math.u-psud.fr> wrote:> My question must be a trivial one. > > There is automatic coercicion to vector when extracting only one line of a > matrix. > # example > A = matrix(1:12,3,4) > rownames(A) = c('a1','a2','a3') > > i = 1:2 > A[i,] > # [,1] [,2] [,3] [,4] > # a1 1 4 7 10 matrix > # a2 2 5 8 11 > > i = 1 > A[i,] > # [1] 1 4 7 10 vector !!! > > # to get the rowname, it is necessary to do > rownames(A)[i] > # [1] "a1" > > Is it possible to get a (1,4)-matrix (without testing length(i) ) ? I see > nothing in options()... > > Jean Coursol > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. >[[alternative HTML version deleted]]
This is Circle 8.1.44 of 'The R Inferno'. http://www.burns-stat.com/documents/books/the-r-inferno/ Pat On 21/03/2015 11:04, Jean.Coursol at math.u-psud.fr wrote:> My question must be a trivial one. > > There is automatic coercicion to vector when extracting only one line of a > matrix. > # example > A = matrix(1:12,3,4) > rownames(A) = c('a1','a2','a3') > > i = 1:2 > A[i,] > # [,1] [,2] [,3] [,4] > # a1 1 4 7 10 matrix > # a2 2 5 8 11 > > i = 1 > A[i,] > # [1] 1 4 7 10 vector !!! > > # to get the rowname, it is necessary to do > rownames(A)[i] > # [1] "a1" > > Is it possible to get a (1,4)-matrix (without testing length(i) ) ? I see > nothing in options()... > > Jean Coursol > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. >
See the help page for the "[" operator ... ?"[" ... and use the drop parameter as in: A[1,,drop=FALSE] [,1] [,2] [,3] [,4] a1 1 4 7 10 B. On Mar 21, 2015, at 8:10 AM, J Robertson-Burns <robertsonburns at btinternet.com> wrote:> This is Circle 8.1.44 of 'The R Inferno'. > > http://www.burns-stat.com/documents/books/the-r-inferno/ > > Pat > > On 21/03/2015 11:04, Jean.Coursol at math.u-psud.fr wrote: >> My question must be a trivial one. >> >> There is automatic coercicion to vector when extracting only one line of a >> matrix. >> # example >> A = matrix(1:12,3,4) >> rownames(A) = c('a1','a2','a3') >> >> i = 1:2 >> A[i,] >> # [,1] [,2] [,3] [,4] >> # a1 1 4 7 10 matrix >> # a2 2 5 8 11 >> >> i = 1 >> A[i,] >> # [1] 1 4 7 10 vector !!! >> >> # to get the rowname, it is necessary to do >> rownames(A)[i] >> # [1] "a1" >> >> Is it possible to get a (1,4)-matrix (without testing length(i) ) ? I see >> nothing in options()... >> >> Jean Coursol >> >> ______________________________________________ >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see >> 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. >> > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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.