[R] if statement problem

[Domenico Vistocco]

You should look for your answer using the help for the if statement (?"if").
The cond argument should be a scalar (otherwise only the first element 
is used).

?"if"
.....
 cond: A length-one logical vector that is not 'NA'. Conditions of
          length greater than one are accepted with a warning, but only
          the first element is used.  Other types are coerced to
          logical if possible, ignoring any class.
...

The ifelse statement check the condition for each element of your input 
(returning
a value with the same shape).

domenico

Gerard Smits wrote:
> Hi All,
>
> I have a small dataset named das  (43 cases) in which I am trying to 
> create a binary outcome (1/0) based on the following code:
>
> if (das$age>65 && das$bmi>30) {das$danger<-1} else das$danger<-0
>
> I am setting a flag called 'danger' to 1 of the subject is over 65 
> and has a BMI > 30.
>
> I find that my statement evaluates the first record in the data.frame 
> and then carries that assignment for all. I detected this as I played 
> around with the values and found that the T/F status of the first 
> record was always carried dowqn. I have gotten this to work with an 
> elseif construction, but would like to know what is happening here.
>
> Thanks,
>
> Gerard
>
> Using: Windows Vista and R 2.61
>
>
> Code and output:
>
> das<- sasxport.get("c:\\personal\\r\\das.xpt")
> if (das$age>65 && das$bmi>30) {das$danger<-1} else das$danger<-0
> attach(das)
> das
>
>
>          The following object(s) are masked from das ( position 3 ) :
>
>           age bmi day id male sex status
>
>        id age sex  bmi status day male danger
> 1  33001  35   M 27.5      0 365    1      0
> 2  33002  29   M 34.9      1  22    1      0
> 3  33003  41   F 23.6      0 365    0      0
> 4  33004  55   F 27.0      0 365    0      0
> 5  42001  37   M 39.0      0 365    1      0
> 6  42002  53   M 26.6      1 124    1      0
> 7  42003  46   F 45.4      1 287    0      0
> 8  42004  35   F 36.2      0 365    0      0
> 9  42005  38   F 24.6      0 365    0      0
> 10 42006  58   F 28.0      0 365    0      0
> 11 42007  27   M 25.0      0 365    1      0
> 12 42008  65   F 24.6      0 365    0      0
> 13 42009  25   F 28.0      0 365    0      0
> 14 43001  66   M 27.8      0 365    1      0
> 15 43002  57   F 34.0      0 365    0      0
> 16 43003  45   F 38.1      0 365    0      0
> 17 43004  33   F 53.3      1  62    0      0
> 18 43005  56   F 36.5      0 365    0      0
> 19 43006  31   F 22.4      1   1    0      0
> 20 43007  53   F 32.2      1  21    0      0
> 21 55001  51   M 29.2      0 365    1      0
> 22 55002  33   F 18.7      0 365    0      0
> 23 55003  40   F 30.3      0 365    0      0
> 24 55004  67   M 31.9      0 365    1      0 <- Problem case should 
> =1 for danger
> 25 55005  41   F 35.0      0 365    0      0
> 26 55006  44   F 37.3      0 365    0      0
> 27 55007  67   M 28.4      1   1    1      0
> 28 55008  65   F 28.8      0 365    0      0
> 29 55009  76   M 18.8      1 225    1      0
> 30 55010  75   F 21.1      1  39    0      0
> 31 63001  30   F 24.9      0 365    0      0
> 32 63002  36   F 47.2      1 377    0      0
> 33 63003  45   F 32.0      0 365    0      0
> 34 63004  49   F 32.3      0 365    0      0
> 35 63005  41   F 20.2      0 365    0      0
> 36 63006  60   F 28.2      0 365    0      0
> 37 63007  33   F 24.5      0 365    0      0
> 38 63008  36   F 28.4      1  56    0      0
> 39 63009  31   F 22.1      0 365    0      0
> 40 63010  77   M 26.6      1   9    1      0
> 41 63011  41   F 32.0      0 365    0      0
> 42 63012  40   F 38.5      1  92    0      0
> 43 63013  27   M 20.6      0 365    1      0
>
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