On Nov 26, 2009, at 12:17 AM, David Winsemius wrote:
On Nov 25, 2009, at 9:54 PM, Michael Ash wrote:
I remain confused by the difference between
library(MASS)
data(Cars93)
as
.data
.frame
(tapply
(Cars93
$Price,list(Cars93$Origin,Cars93$AirBags,Cars93$Passengers),median))
as
.data
.frame
.table
(tapply
(Cars93
$Price,list(Cars93$Origin,Cars93$AirBags,Cars93$Passengers),median))
The display may not make it clear, but applying str() to both should
make it clear that the first is similar to what one might get with
cbind'ing the results of the inner function (which would not work in
this case on a list object).
I mis-wrote... tapply returned an array, although not one that would
allow simple cbinding. Ths is the code from as.data.frame.array, x
being the passed object:
dn <- dimnames(x)
dim(x) <- c(d[1L], prod(d[-1L]))
if (!is.null(dn)) {
if (length(dn[[1L]]))
rownames(x) <- dn[[1L]]
for (i in 2L:length(d)) if (is.null(dn[[i]]))
dn[[i]] <- seq_len(d[i])
colnames(x) <- interaction(expand.grid(dn[-1L]))
}
as.data.frame.matrix(x, row.names, optional, ...)
You get two rows of 18 variables all medians or NA, while the second
is the unique combinations of the (USA/
nonUSA)*(Passengers)*(Airbags)*(Passengers) cross and their
associated medians which as.data.frame has labeled "Freq" since that
is the usual element of a contingency table. I think of
as.data.frame.table as simply another way of accomplishing
as.data.frame(table()). Is that not how you were intending it?
I clearly want the latter, but that's not clear from the
documentation.
Sometimes it is helpful to look at the code as well:
> as.data.frame.table
function (x, row.names = NULL, ..., responseName = "Freq",
stringsAsFactors = TRUE)
{
x <- as.table(x)
ex <- quote(data.frame(do.call("expand.grid", c(dimnames(x),
stringsAsFactors = stringsAsFactors)), Freq = c(x), row.names
= row.names))
names(ex)[3L] <- responseName
eval(ex)
}
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
Best,
Michael
On Wed, Nov 25, 2009 at 5:55 PM, David Winsemius <dwinsem...@comcast.net
> wrote:
On Nov 25, 2009, at 4:11 PM, Michael Ash wrote:
Dear all,
This seems to be working, but I'd like to make sure that I'm not
doing
anything wrong.
I am using by() to construct a complicated summary statistic by
several factors in my data (specifically, the 90-50 income ratio by
city and race).
cityrace.by <- by(microdata, list(microdata$city,microdata$race),
function (x) quantile(x$income, probs=0.9) / quantile(x$income,
probs=0.5) )
I would now like to use the data created by by() as a dataset with
city-race as the unit of observation.
However, cityrace.data <- as.data.frame(cityrace.by) does not
work because
"Error in as.data.frame.default(city.by) :
cannot coerce class "by" into a data.frame"
The following is not a documented use of as.data.frame.table(),
but it
seems to work. It gives the columns slightly strange names,
including
"Freq" for the statistic computed in by by() but otherwise, the
dataframe is indexed by city and race with the 90-50 ratio as the
variable
cityrace.data <- as.data.frame.table(cityrace.by)
If the by-object you get happens to be a 2d array, then why not.
Tables are
matrices after all.
tt <- table(c(1,1), c(1,1))
tt
1
1 2
is.matrix(tt)
[1] TRUE
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
--
Michael Ash, Associate Professor
of Economics and Public Policy
Department of Economics and CPPA
University of Massachusetts
Amherst, MA 01003
Tel +1-413-545-6329 Fax +1-413-545-2921
Email m...@econs.umass.edu
http://people.umass.edu/maash
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
