[R] How to use conditional statement

[Ivan Calandra]

Thanks for the comment, I didn't think about this thorougly.

Le 3/10/2011 12:54, Duncan Murdoch a écrit :
> On 11-03-10 5:54 AM, Ivan Calandra wrote:
>> Try with double "== "instead:
>> ifelse(val3 == "Monthly", val<- val1, val<- val2)
>
> That might work, but it is not how you should do it.  (It should work 
> if val3 has a single entry, but will do strange things if val3 is a 
> vector:
>
> > val3 <- c("Monthly", "Daily")
> > ifelse(val3 == "Monthly", val<- 1, val<- 2)
> [1] 1 2
> > val
> [1] 2
>
>
> The ifelse() function does a vectorized test, and picks results from 
> the two vector alternatives.  Vincy wants a simple logical if, which 
> can be computed in a few different ways:
>
>  val <- if(val3 == "Monthly") val1 else val2
>
> or
>
>  if (val3 == "Monthly") val <- val1
>  else val <- val2
>
> For a simple calculation like this I'd probably use the former; if the 
> calculation got more complex I'd prefer the latter.
>
> Duncan Murdoch
>
>>
>> Single "=" is for setting arguments within a function call. If you want
>> to test equality, then double "==" is required.
>> See ?"=="
>>
>> HTH,
>> Ivan
>>
>> Le 3/10/2011 11:45, Vincy Pyne a écrit :
>>> Dear R helpers
>>>
>>> Suppose
>>>
>>> val1 = c(10, 20, 35, 80, 12)
>>> val2 = c(3, 8, 11, 7)
>>>
>>> I want to select either val1 or val2 depending on value of third 
>>> quantity val3.
>>>
>>> val3 assumes either of the values "Monthly" or "Yearly".
>>>
>>> If val3 = "Monthly", then val = val1 and if val3 = "Yearly", then 
>>> val = val2.
>>>
>>> I tried the ifelse statement as
>>>
>>>
>>> ifelse(val3 = "Monthly", val = val1, val2)
>>>
>>> I get following error
>>>
>>>> ifelse(val3 = "Monthly", val = val1, val2)
>>> Error in ifelse(val3 = "Monthly", val = val1, val2) :
>>>     unused argument(s) (val3 = "Monthly", val = val1)
>>>
>>>> val
>>> Error: object 'val' not found
>>>
>>> Kindly guide.
>>>
>>> Regards
>>>
>>> Vincy
>>>
>>>
>>>
>>>     [[alternative HTML version deleted]]
>>>
>>>
>>>
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>>
>
>

-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. Säugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra at uni-hamburg.de

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