[R] Multiple if function

David Winsemius dwinsemius at comcast.net
Wed Sep 16 02:00:02 CEST 2015 

On Sep 15, 2015, at 4:46 PM, David L Carlson wrote:

> I realize that you can break this approach as well with a suitably complex expression, but I took it as a challenge:
> 
>> dat <- data.frame(ASB = c(LETTERS[1:3]), Flow=c(11.51, 9.2, 10.5), stringsAsFactors=FALSE)
>> cat <- LETTERS[1:3]
>> mult <- c("'*'(2," , "'+'(5,", "sqrt(")
>> sapply(parse(text=paste0(mult[match(dat$ASB, cat)], dat$Flow, ")")), eval)
> [1] 23.02000 14.20000  3.24037

This seems a bit less tortured:

> mapply(  function(x,y) switch(x, A=y*2, B=y+3, C=sqrt(y) ), dat$ASB, dat$Flow )
       A        B        C 
23.02000 12.20000  3.24037 

Best;
The Other David

> 
> David
> 
> -----Original Message-----
> From: Bert Gunter [mailto:bgunter.4567 at gmail.com] 
> Sent: Tuesday, September 15, 2015 4:43 PM
> To: David L Carlson <dcarlson at tamu.edu>
> Cc: Peter Alspach <Peter.Alspach at plantandfood.co.nz>; r-help at r-project.org
> Subject: Re: [R] Multiple if function
> 
> Thanks, David.
> 
> I would say, not quite.
> 
> What if the alternatives are:
> 
> If class = "a" multiply y by 2;
> If class = "b"  add 5 to y;
> If class = "c" take sqrt(y)
> (where y is numeric, say)
> ?
> 
> Cheers,
> Bert
> Bert Gunter
> 
> "Data is not information. Information is not knowledge. And knowledge
> is certainly not wisdom."
>   -- Clifford Stoll
> 
> 
> On Tue, Sep 15, 2015 at 2:11 PM, David L Carlson <dcarlson at tamu.edu> wrote:
>> You could use match() and avoid ifelse():
>> 
>>> dat <- data.frame(ASB = c(LETTERS[1:3]), Flow=c(11.51, 9.2, 10.5), stringsAsFactors=FALSE)
>>> cat <- LETTERS[1:3]
>>> mult <- c(.1, .15, .2)
>>> dat$Flow * mult[match(dat$ASB, cat)]
>> [1] 1.151 1.380 2.100
>> 
>> -------------------------------------
>> David L Carlson
>> Department of Anthropology
>> Texas A&M University
>> College Station, TX 77840-4352
>> 
>> 
>> -----Original Message-----
>> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Bert Gunter
>> Sent: Tuesday, September 15, 2015 3:51 PM
>> To: Peter Alspach
>> Cc: r-help at r-project.org
>> Subject: Re: [R] Multiple if function
>> 
>> ... but this only works if ASBclass is numeric. What if it is a factor
>> (or even character)?
>> 
>> One can always finesse factors in simple cases like this, but for 2
>> reasons, I don't think it's a good idea.
>> 
>> 1. One should make use of a factor's API, rather than its internal
>> integer representation(which, I grant, ain't likely to change);
>> 
>> 2. For more complicated alternatives (e.g. entirely different
>> functions depending on the factor value) it won't work anyway.
>> 
>> For simple cases, ifelse() seems reasonable; but for more alternatives
>> -- say 10 or 50 -- this becomes too cumbersome (imho). I think the
>> split and recombine approach then becomes the best option, but maybe
>> there is some easier, shorter, approach that I am overlooking. Please
>> correct me if this is the case.
>> 
>> Best,
>> Bert
>> 
>> 
>> 
>> 
>> 
>> 
>> Bert Gunter
>> 
>> "Data is not information. Information is not knowledge. And knowledge
>> is certainly not wisdom."
>>   -- Clifford Stoll
>> 
>> 
>> On Tue, Sep 15, 2015 at 12:23 PM, Peter Alspach
>> <Peter.Alspach at plantandfood.co.nz> wrote:
>>> Tena koe Maria
>>> 
>>> It seems you need to multiply Flow by 0.05+ASBClass/20 (i.e., no if calls are necessary)
>>> 
>>> HTH ....
>>> 
>>> Peter Alspach
>>> 
>>> -----Original Message-----
>>> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Maria Lathouri
>>> Sent: Tuesday, 15 September 2015 10:57 p.m.
>>> To: r-help at r-project.org
>>> Subject: [R] Multiple if function
>>> 
>>> Dear all,
>>> 
>>> I am writing as I would like your help. I have a dataframe with two columns, ASB and Flow, where the the first one has values 1, 2 or 3 and the second flow data. Something like that:
>>> ASBclass    Flow1              11.51               9.2
>>> 2              10.5
>>> 3               6.7  ...              ...
>>> I would like to produce a third column named eg. deviation where it would get me values based on if ASBclass is 1, multiply Flow by 0.1; if ASBclass is 2 then multiply Flow by 0.15 and if ASBclass is 3 then multiply by 0.2.
>>> 
>>> If (ASBclass=1) { deviation<-Flow*0.1}
>>> If (ASBclass=2) { deviation<-Flow*0.15}If (ASBclass=1) { deviation<-Flow*0.2} I am not sure whether I should add the else function and how can I combine these separate functions.
>>> 
>>> Can anyone help me on that?
>>> Thank you very much.
>>> 
>>> Kind regardsMaria
>>> 
>>>        [[alternative HTML version deleted]]
>>> 
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>> 
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> 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 at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.

David Winsemius
Alameda, CA, USA

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