On Jan 28, 2010, at 12:08 PM, Marc Schwartz wrote:
On Jan 28, 2010, at 10:04 AM, David Winsemius wrote:
On Jan 28, 2010, at 10:55 AM, Marc Schwartz wrote:
Ivan,
The default behavior for print()ing objects to the console in an R
session is via the use of the print.* methods. For real numerics,
print.default() is used and the format is based upon the number of
significant digits, not the number of decimal places. There is
also an interaction with par("scipen"), which influences when
scientific notation is used. See ?print.default for more
information on defaults and behavior, taking note of the 'digits'
argument, which is influenced by options("digits").
Importantly, you need to differentiate between how R stores
numeric real values and how it displays or prints them.
Internally, R stores real numbers using a double precision data
type by default.
The internal storage is not truncated by default and is stored to
full precision for doubles, within binary representation limits.
You can of course modify the values using functions such as
round() or truncate(), etc. See ?round for more information.
For display, Peter has already pointed you to sprintf() and
related functions, which allow you to format output for "pretty
printing" to things like column aligned tables and such. Those do
not however, affect the default output to the R console.
If one alters print.default, one can get different behavior, for
instance:
print.default <- function (x, digits = NULL, quote = TRUE, na.print
= NULL, print.gap = NULL,
right = FALSE, max = NULL, useSource = TRUE, ...)
{if (is.numeric(x)) {x <- as.numeric(sprintf("%7.3f", x))}
noOpt <- missing(digits) && missing(quote) && missing(na.print) &&
missing(print.gap) && missing(right) && missing(max) &&
missing(useSource) && length(list(...)) == 0L
.Internal(print.default(x, digits, quote, na.print, print.gap,
right, max, useSource, noOpt))
}
This will have the requested effect for numeric vectors, but does
not seem to be altering the behavior of print.data.frame().
print(ac2)
score pt times trt
1 28.825139 1 0 1
2 97.458521 1 3 1
3 26.217289 1 6 1
4 80.636507 2 0 1
5 99.729364 2 3 1
6 85.812312 2 6 1
7 2.515870 3 0 1
8 3.893545 3 3 1
9 55.666848 3 6 1
10 21.966027 4 0 1
print(ac2$score)
[1] 28.825 97.459 26.217 80.637 99.729 85.812 2.516 3.894 55.667
21.966
David,
The issue there is that when printing the vector, you are using
print.default() directly, so you get the desired result with a
numeric vector.
Thanks, Marc;
I do understand. I had been hoping that there might be a "final common
pathway" to use a biochemistry analogy, at least for numeric objects,
but it appears not.
--
David.
When you print the data frame, internally print.data.frame() calls
format.data.frame(), which then internally uses format() on a column-
by-column basis and there is the rub. format() brings you back to
using significant digits on numeric vectors and of course returns a
character vector. By the time the output is actually print()ed to
the console, the original data frame has been converted to a
formatted character matrix and that is what gets printed.
str(format.data.frame(ac2))
'data.frame': 10 obs. of 4 variables:
$ score:Class 'AsIs' chr [1:10] "28.825139" "97.458521" "26.217289"
"80.636507" ...
$ pt :Class 'AsIs' chr [1:10] "1" "1" "1" "2" ...
$ times:Class 'AsIs' chr [1:10] "0" "3" "6" "0" ...
$ trt :Class 'AsIs' chr [1:10] "1" "1" "1" "1" ...
str(format.data.frame(ac2, digits = 2))
'data.frame': 10 obs. of 4 variables:
$ score:Class 'AsIs' chr [1:10] " 28.8" " 97.5" " 26.2" " 80.6" ...
$ pt :Class 'AsIs' chr [1:10] "1" "1" "1" "2" ...
$ times:Class 'AsIs' chr [1:10] "0" "3" "6" "0" ...
$ trt :Class 'AsIs' chr [1:10] "1" "1" "1" "1" ...
This is why changing print.default() by itself is not sufficient.
Other object classes are formatted and printed in varying ways and
print methods have been defined for them which may not use it
directly.
HTH,
Marc Schwartz
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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