[Bioc-devel] simple question about floor

Yes, floating point issue.

See e.g. 

http://cran.r-project.org/doc/FAQ/R-FAQ.html
7.31 Why doesn't R think these numbers are equal?

options(digits = 22)
29/50

[1] 0.579999999999999960032

29/50 * 50

[1] 28.99999999999999644729

29*50/50

[1] 29.00000000000000000000

.58 * 50

[1] 28.99999999999999644729

floor(28.999999)

[1] 28.00000000000000000000

floor(29.000000)

[1] 29.00000000000000000000

Steven McKinney

Statistician
Molecular Oncology and Breast Cancer Program
British Columbia Cancer Research Centre

-----Original Message-----
From: bioc-devel-bounces at r-project.org [mailto:bioc-devel-bounces at r-
project.org] On Behalf Of Ou, Jianhong
Sent: December-19-13 1:53 PM
To: bioc-devel at r-project.org
Subject: [Bioc-devel] simple question about floor

Hi all,

Maybe this is not a bioconductor question but R. However, I feel this is
very interesting.

I tried

floor(29/50*50)

[1] 28

floor(29*50/50)

[1] 29

Is this a floating-point problem? How could we explain this?

Yours sincerely,

Jianhong Ou

LRB 670A
Program in Gene Function and Expression
364 Plantation Street Worcester,
MA 01605

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