Because a data frame can hold different data types (even matrices) in different variables, one row of it can not be converted to a vector in general (where all elements need to be of the same type).
Andy > From: Fernando Saldanha > > Thanks, it's interesting reading. > > I also noticed that > > sw[, 1, drop = TRUE] is a vector (coerces to the lowest dimension) > > but > > sw[1, , drop = TRUE] is a one-row data frame (does not convert it into > a list or vector) > > FS > > > On 4/16/05, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > > You should look at > > > > > ?"[" > > > > and look very carefully at the "drop" argument. For your example > > > > > sw[, 1] > > > > is the first component of the data frame, but > > > > > sw[, 1, drop = FALSE] > > > > is a data frame consisting of just the first component, as > > mathematically fastidious people would expect. > > > > This is a convention, and like most arbitrary conventions > it can be very > > useful most of the time, but some of the time it can be a very nasty > > trap. Caveat emptor. > > > > Bill Venables. > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of > Fernando Saldanha > > Sent: Saturday, 16 April 2005 1:07 PM > > To: Submissions to R help > > Subject: [R] Getting subsets of a data frame > > > > I was reading in the Reference Manual about Extract.data.frame. > > > > There is a list of examples of expressions using [ and [[, with the > > outcomes. I was puzzled by the fact that, if sw is a data > frame, then > > > > sw[, 1:3] > > > > is also a data frame, > > > > but > > > > sw[, 1] > > > > is just a vector. > > > > Since R has no scalars, it must be the case that 1 and 1:1 > are the same: > > > > > 1 == 1:1 > > [1] TRUE > > > > Then why isn't sw[,1] = sw[, 1:1] a data frame? > > > > FS > > > > ______________________________________________ > > [email protected] mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! > > http://www.R-project.org/posting-guide.html > > > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > > > ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
