On 26/04/2014, 4:12 PM, Tom Kraljevic wrote:
Hi,
One additional follow-up here.
Unfortunately, I hit what looks like an R parsing bug that makes the Java
Double.toHexString() output
unreliable for reading by R. (This is really unfortunate, because the format
is intended to be lossless
and it looks like it’s so close to fully working.)
You can see the spec for the conversion here:
http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#toHexString(double)
The last value in the list below is not parsed by R in the way I expected, and
causes the column to flip
from numeric to factor.
-0x1.8ff831c7ffffdp-1
-0x1.aff831c7ffffdp-1
-0x1.bff831c7ffffdp-1
-0x1.cff831c7ffffdp-1
-0x1.dff831c7ffffdp-1
-0x1.eff831c7ffffdp-1
-0x1.fff831c7ffffdp-1 <<<<< this value is not parsed as a number and
flips the column from numeric to factor.
That looks like a bug in the conversion code. It uses the same test for
lack of accuracy for hex doubles as it uses for decimal ones, but hex
doubles can be larger before they lose precision. I believe the largest
integer that can be represented exactly is 2^53 - 1, i.e.
0x1.fffffffffffffp52
in this notation; can you confirm that your Java code reads it and
writes the same string? This is about 1% bigger than the limit at which
type.convert switches to strings or factors.
Duncan Murdoch
Below is the R output from adding one row at a time to “bad.csv”.
The last attempt results in a factor rather than a numeric column.
What’s really odd about it is that the .a through .e case work fine but the .f
case doesn’t.
Thanks,
Tom
bad.df = read.csv(file="/Users/tomk/bad.csv", header=F)
str(bad.df)
'data.frame': 1 obs. of 1 variable:
$ V1: num -0.781
bad.df = read.csv(file="/Users/tomk/bad.csv", header=F)
str(bad.df)
'data.frame': 2 obs. of 1 variable:
$ V1: num -0.781 -0.844
bad.df = read.csv(file="/Users/tomk/bad.csv", header=F)
str(bad.df)
'data.frame': 3 obs. of 1 variable:
$ V1: num -0.781 -0.844 -0.875
bad.df = read.csv(file="/Users/tomk/bad.csv", header=F)
str(bad.df)
'data.frame': 4 obs. of 1 variable:
$ V1: num -0.781 -0.844 -0.875 -0.906
bad.df = read.csv(file="/Users/tomk/bad.csv", header=F)
str(bad.df)
'data.frame': 5 obs. of 1 variable:
$ V1: num -0.781 -0.844 -0.875 -0.906 -0.937
bad.df = read.csv(file="/Users/tomk/bad.csv", header=F)
str(bad.df)
'data.frame': 6 obs. of 1 variable:
$ V1: num -0.781 -0.844 -0.875 -0.906 -0.937 ...
bad.df = read.csv(file="/Users/tomk/bad.csv", header=F)
str(bad.df)
'data.frame': 7 obs. of 1 variable:
$ V1: Factor w/ 7 levels "-0x1.8ff831c7ffffdp-1",..: 1 2 3 4 5 6 7
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