[R] Multiple if function

[David L Carlson]

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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