[R] Multiple if function
Jeff Newmiller
jdnewmil at dcn.davis.CA.us
Wed Sep 16 00:12:03 CEST 2015
If dat is large and you want to be efficient about this, then compute only the answers you need and put them right where they belong as you go:
dat$result <- NA
idx <- "A" == dat$ASB
dat$result[ idx ] <- 2 * dat$Flow[ idx ]
idx <- "B" == dat$ASB
dat$result[ idx ] <- 5 + dat$Flow[ idx ]
idx <- "C" == dat$ASB
dat$result[ idx ] <- sqrt( dat$Flow[ idx ] )
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On September 15, 2015 2:42:42 PM PDT, Bert Gunter <bgunter.4567 at gmail.com> wrote:
>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.
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