Getting subsets of a data frame
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, Bill.Venables at csiro.au <Bill.Venables at csiro.au> 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: r-help-bounces at stat.math.ethz.ch [mailto:r-help-bounces at stat.math.ethz.ch] 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
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