[R] trouble understanding why ...=="NaN" isn't true

[Bert Gunter]

1. "NaN" is a character string, **not** NaN; hence is.nan("NaN") yields
FALSE.

2. Please read the docs!  ?NaN explicitly says:

"Do not test equality to NaN, or even use identical, since systems typically
have many different NaN values."


Bert Gunter
Genentech Nonclinical Statistics


-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Andrew Yee
Sent: Tuesday, May 29, 2007 3:33 PM
To: r-help at stat.math.ethz.ch
Subject: [R] trouble understanding why ...=="NaN" isn't true

I have the following data:

> dataset[2,"Sample.227"]
[1]    NaN
1558 Levels: -0.000 -0.001 -0.002 -0.003 -0.004 -0.005 -0.006 -0.007 -0.008-
0.009 ...  2.000


However, I'm not sure why this expression is coming back as FALSE:

> dataset[2,"Sample.227"]=="NaN"
[1] FALSE

Similarly:

> dataset[2,"Sample.227"]==NaN
[1] NA


It seems that since "NaN" is represented as a character, this expression
=="NaN" should be TRUE, but it's returning as FALSE.

Thanks,
Andrew

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