Hello,
This seems to be a case for FAQ 7.31 Why doesn't R think these numbers
are equal?
See this example:
3/5 - 1/5 - 2/5 # not zero
3/5 - (1/5 + 2/5) # not zero, different from above
In your case, try
for(idx in breaks){
print(idx / interval, digits = 16) # see problem indices
bins[idx / interval] = idx
}
b2 <- breaks
identical(bins, b2) # FALSE
What happens is that instead of 7, the value of idx/interval is
6.9999999 with integer part 6. So bins[6] is assigned twice, first 1.2
then this valuew is overwritten by 1.4 and bins[7] is never written to.
The same goes with indices 9 and 10.
Avoid this type of indexing. And if possible use the vectorized
instruction b2 <- breaks.
Hope this helps,
Rui Barradas
Em 06-10-2012 07:14, 周果 escreveu:
Hi there,
Here is a minimum working example:
----------------------------------------------------------------
lower = 0
upper = 1
n_bins = 50
interval = (upper - lower) / n_bins
bins = vector(mode="numeric", length=n_bins)
breaks = seq(from=lower + interval, to=upper, by=interval)
for(idx in breaks)
{
bins[idx / interval] = idx
}
print(bins)
----------------------------------------------------------------
which outputs:
----------------------------------------------------------------
[1] 0.02 0.04 0.06 0.08 0.10 0.14 0.00 0.16 0.20 0.00 0.22 0.24 0.26 0.28
[15] 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56
[29] 0.58 0.60 0.62 0.64 0.66 0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82 0.84
[43] 0.86 0.88 0.90 0.92 0.94 0.96 0.98 1.00
----------------------------------------------------------------
It turns out that some elements are incorrect, such as the 6th
element 0.14, which should be 0.12 in fact.
Is this a bug or I am missing something?
And here is the output of sessionInfo():
----------------------------------------------------------------
R version 2.15.0 (2012-03-30)
Platform: x86_64-pc-mingw32/x64 (64-bit)
locale:
[1] LC_COLLATE=Chinese (Simplified)_People's Republic of China.936
[2] LC_CTYPE=Chinese (Simplified)_People's Republic of China.936
[3] LC_MONETARY=Chinese (Simplified)_People's Republic of China.936
[4] LC_NUMERIC=C
[5] LC_TIME=Chinese (Simplified)_People's Republic of China.936
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] cubature_1.1-1 tools_2.15.0
----------------------------------------------------------------
Thanks in advance.
Regards,
Guo
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