Re: [R] Why can't R understand if(num!=NA)?
On May 3, 2013, at 21:36 , David Winsemius wrote: On May 3, 2013, at 10:46 AM, peter dalgaard wrote: Because comparison with an unknown value yields an unknown result. Anything else would violate the Second Law of Thermodynamics. We cannot have comparisons reducing entropy, now can we? Uncertainty cannot run uphill. Now what does this say about SAS, where the missing value is smaller than all regular numbers? I.e., DATA; iteen = (age 20); turns people of unknown age into instant teenagers. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd@cbs.dk Priv: pda...@gmail.com __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
On May 3, 2013, at 10:58 PM, peter dalgaard wrote: On May 3, 2013, at 21:36 , David Winsemius wrote: On May 3, 2013, at 10:46 AM, peter dalgaard wrote: Because comparison with an unknown value yields an unknown result. Anything else would violate the Second Law of Thermodynamics. We cannot have comparisons reducing entropy, now can we? Uncertainty cannot run uphill. Now what does this say about SAS, where the missing value is smaller than all regular numbers? I.e., DATA; iteen = (age 20); turns people of unknown age into instant teenagers. And are handled as zero when included in calculations using SUM ( as, I also read, does SPSS). So SAS comparisons are still increasing entropy. Quantum mechanics says there is no real vacuum state, so maybe that's where those not-really-missing missing values are ending up after they confound our notions of existence. -- David Winsemius Alameda, CA, USA __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
[R] Why can't R understand if(num!=NA)?
I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Thanks, Miao [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
-Original Message-
if(num!=NA)
it yields an error message.
Why doesn't the first statement work?
Because you just compared something with NA (usually interpreted as 'missing')
and because of that the comparison result is also NA.
'if' then tells you that you have a missing value where you need either TRUE or
FALSE.
Play with
num!=NA #returns NA
and
if(NA) Not there #returns error
is.na() returns TRUE for NA's, so 'if' knows what to do with the answer.
S Ellison
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Re: [R] Why can't R understand if(num!=NA)?
You can use only if(!is.na(num)) [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
A logical operation involving NA returns NA, never TRUE or FALSE: See the 8th Circle of the R Inferno (8.1.4): http://www.burns-stat.com/pages/Tutor/R_inferno.pdf num - 1 num==NA [1] NA is.na(num) [1] FALSE - David L Carlson Associate Professor of Anthropology Texas AM University College Station, TX 77840-4352 -Original Message- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of jpm miao Sent: Friday, May 3, 2013 10:25 AM To: r-help Subject: [R] Why can't R understand if(num!=NA)? I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Thanks, Miao [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
On May 3, 2013, at 10:24 AM, jpm miao miao...@gmail.com wrote: I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Thanks, Miao NA is undefined: NA == NA [1] NA NA != NA [1] NA Therefore the equality you are attempting does not return a TRUE or FALSE result, it is unknown and NA is returned. ?is.na was designed specifically to test for the presence of an NA value and return a TRUE or FALSE result which can then be tested. See: http://cran.r-project.org/doc/manuals/r-release/R-intro.html#Missing-values Regards, Marc Schwartz __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
On May 3, 2013, at 8:24 AM, jpm miao wrote: I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Read the manual: ?NA -- David Winsemius Alameda, CA, USA __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
On 03-05-2013, at 17:24, jpm miao miao...@gmail.com wrote: I have a program, when I write if(num!=NA) it yields an error message. it? What is unclear about the error message? However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Read section 2.5 'Missing values of the manual An Introduction to R. Berend Thanks, Miao [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
num1- c(0,NA,1,3) num1==NA #[1] NA NA NA NA num1!=NA #[1] NA NA NA NA is.na(num1) #[1] FALSE TRUE FALSE FALSE A.K. - Original Message - From: jpm miao miao...@gmail.com To: r-help r-help@r-project.org Cc: Sent: Friday, May 3, 2013 11:24 AM Subject: [R] Why can't R understand if(num!=NA)? I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Thanks, Miao [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
if(num!=NA)
Why doesn't the first statement work?
An NA value means that the value is unknown. E.g.,
age - NA
means the you do not know the age of your subject.
(The subject has an age, NA means you did not collect
that data.) Thus you do not know the value of
age == 6
either, the subject might be 6 or it might not be.
Hence R makes the value of age==6 NA.
Since R does not have different evaluation rules for literal values
and expressions that means that NA==6 and NA==someAge
must evaluate to NA as well.
The second part of the question is why
if (NA) { } else { }
causes an error. It is a bit arbitrary, but there is a mismatch
between a 2-way 'if' statement and 3-valued logical data
and R deals with it by insisting that the condition in
if (condition) { } else {}
be either TRUE or FALSE, not NA.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
-Original Message-
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf
Of jpm miao
Sent: Friday, May 03, 2013 8:25 AM
To: r-help
Subject: [R] Why can't R understand if(num!=NA)?
I have a program, when I write
if(num!=NA)
it yields an error message.
However, if I write
if(is.na(num)==FALSE)
it works.
Why doesn't the first statement work?
Thanks,
Miao
[[alternative HTML version deleted]]
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Re: [R] Why can't R understand if(num!=NA)?
At a minimum, the first statement needs ==. Also, is.na() gives TRUE/FALSE. While a logical comparison to NA gives NA as a value. Kevin On Fri, May 3, 2013 at 10:24 AM, jpm miao miao...@gmail.com wrote: I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Thanks, Miao [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. -- Kevin Wright [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
On May 3, 2013, at 17:24 , jpm miao wrote: I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Because comparison with an unknown value yields an unknown result. By the way, comparing a logical value to FALSE is silly: if ( !is.na(num) ) will do it. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd@cbs.dk Priv: pda...@gmail.com __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
On May 3, 2013, at 17:24 , jpm miao wrote: I have a program, when I write if(num!=NA) snipped On May 3, 2013, at 10:46 AM, peter dalgaard wrote: Because comparison with an unknown value yields an unknown result. Anything else would violate the Second Law of Thermodynamics. We cannot have comparisons reducing entropy, now can we? Uncertainty cannot run uphill. -- David Winsemius Alameda, CA, USA __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Why can't R understand if(num!=NA)?
On May 3, 2013, at 10:46 AM, peter dalgaard wrote: On May 3, 2013, at 17:24 , jpm miao wrote: I have a program, when I write if(num!=NA) it yields an error message. However, if I write if(is.na(num)==FALSE) it works. Why doesn't the first statement work? Because comparison with an unknown value yields an unknown result. Anything else would violate the Second Law of Thermodynamics. We cannot have comparisons reducing entropy, now can we? Uncertainty cannot run uphill. -- David Winsemius Alameda, CA, USA __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
